Let's let this group of kind posters read your responses to two posts in the Polyamory Support Group. I have cut and pasted here.

"How much do your family and friends have to know before you yourself are certain? We're taking our time, ourselves. Our 3rd does attend certain events and outings with us, and we attend hers, and we introduce each other as family friends. It's not meant to be an equivocation -- it gives our family, friends and acquaintances a chance to meet and see us as people before asking them to wrap their head around an unfamiliar cultural pattern."

and

"I don't know enough the particulars of your situation to know if my thoughts can apply, but one thing that worked for us was giving our kids a relationship with our "friend" -- meals out, hanging out at track meets, picnics, etc. -- before explaining that we were expanding our dyadic relationship to a triadic one. (We're fortunate that our eldest has a penchant for Greek and Latin.) We avoided using the term "polyamory" because that is technically an open-ended term, and we didn't want our kids to feel like lots of people would be walking in and out of our family. We are (at least now) just three, so we gave our kids the security of accuracy.
Recently we were talking about letting my husband's family know, and I mentioned that they too should meet our 3rd first and let them appreciate her as a person, before springing the whole unfamiliar concept on them. Our eldest overheard us and mentioned that it had really helped him.
Again, I don't know how far this could apply to you, but I hope it helps some."

Ditto to rmb.

I pray that you find the strength to fight against this and live life on the terms YOU find acceptable.

If that is not possible, I pray that you find a way to reduce the pain and hurt you are now feeling without it being detrimental to your health and well being. Perhaps check out the Infidelity or Betrayed Spouses forums for additional support.

It's your right to choose and I see why you may be "looking on the bright side." In some way this person is helping you take care of something you feel you are not able to do. I worry that over time (if not already), you will be looked at as the "cash cow." It hurts being used. They will probably end up being a couple and you will be an outsider. I see no way of this strengthening your marriage.

Best of luck to you.

I don't know the extent of your medical problems, but from what you wrote it doesn't seem that you lack insight or capacity to take care of your medical problems, because you are deeply invested into this situation with your h.
It seems to me that THIS issue is actually counterproductive to you focusing on taking care of yourself.
I live alone and have a whole list of things that needs to be done every day in order for me to function and work. Relationship drama only seems to take away from my number one priority - to keep my health intact so I can work and study.
Is she really helpful to you ?
I understand you love your husband , but sometimes love is just not enough. You have to get love in return.
I have to second RMB - this was kinda forced upon you.
It's not fair. Decisions have been made before you had a chance to consent .

PS - the decisions made without your consent would also make me wonder what else they are going to come up with? What if they decided at some point that you are no longer wanted in this triad?

I would not. I am sorry I don't agree being honest is the way to look at it....The guy just wants his cake and eat it too. If you are ill and you took your marriage vows it says you and he agree through Sickness and in health...I would tell him if he needs another woman in our marriage then he should think about leaving. Truthfully if you are disabled and I don't know his income, but you can probably have more if you were not married. If you on disability, you can get additional things offered by the government. Also, if you divorce, he will be have to give you Support Money, also since your disabled he will have to support you in the lifestyle you have now. You have to ask yourself, how can you handle him with another woman. Sorry be he seem like a asshole. If you agree to this, the stress will add to your illness. Go talk to an attorney. Don't be shy. Ask for everything you can get. You can talk to an attorney free for consult.. if you divorce, he is responsible for the attorney fees ....Please think better about yourself. You may be ill but your still a beautiful person and deserve more....Trust me I have gone though something like that, You can have a life without him. He does not deserve you at all...Good Luck...Sorry but this is a horrible way for a husband to treat his wife....He can have sex on his own....

"I have a chronic illness, and my husband is sure that the only way he can support me through it is if we have a triadic relationship"
Well a triad is exactly what it says... are you in a sexual "relationship" with her too? If not, he's in an open relationship of his own.
A triad is when everyone is dating or married to each other...
So, what's your medical condition? And why is this the only way he can support you? Did your vagina fall out? Seriously I have heard a lot of BS why men want permission to have sex with other women but that takes the cake!
BTW if I had an illness that kept me from being able to have sex with my husband he would have my permission to find physical company somewhere else. What you are talking about is emotional and physical... I couldn't deal with that!

There is having a chronic condition or disease you must manage and then there is living like a sick person. The latter is a mind set. Do not live like a sick person. And do not let anyone convince you that you are somehow insufficient, and that someone includes you. Get angry. It's a great motivator for getting some clarity about your situation. And it can help how you navigate your health. I've been sicker than sick at times with my condition but I'll be damned if I forget who the hell I am and how I want to live.

To answer calirn13's question, no, she and I don't have a sexual relationship, but we are developing a a friendship. I'm a person who likes intimate friendships, but has no idea how to take a friendly acquaintance and nurture it to the level of friendship that strengthens me. (Small talk, even when it's pleasant in the moment, drains me.) I have been without an intimate friend, besides my husband, since we moved here 10 years ago. She's a person who sets a lot of store by friendships, put's a lot of energy into them, and who is delighted to have a new friend who likes quiet activities and deep discussions (as compared to the dancing and drinking that's more commonly vaunted in our neck of the woods). I have to admit, it's been kinda nice to have a relationship where we can just leap into heart-baring discussions, without me trying to figure out if it's okay or how to get us there. Just last night we all got together for a dinner and game night, and then had a discussion afterwards, where I spoke about my feelings of betrayal and jealousy and fear, and they listened and heard me. I know they did. She confessed her feelings of being an "interloper" and not knowing if she was doing more good than harm, and not wanting to lose either of us. I know, in print, it sounds unbelievable; I anticipate and appreciate your skepticism. None of us have a framework for believing this. But I was there, and I will vouch for her sincerity. The only commitment that came out of the discussion is that we would give it more time, and that I would feel safer to be open with them about my doubts and fears. But I think we all felt heard.
Also, since the detail seems important to you, my husband and I still have sex. But my illness has meant that I haven't been able to keep up with my husband, for whom sex is an integral part of his self-image. Interestingly, the shock of this did push me me press my gynecologist for a more effective treatment, and she updated a medication and referred me to physical therapy, which has been VERY beneficial. (Sadly my PT has since moved away, but I have a better idea of how to help myself now.)
My husband is also more aware of and willing to talk about his, well, let's just call them "flaws" for shorthand. It like it's allowed him to triangulate on the places in him that need work. (pun intended)

rmb -- I am usually the first person to convince me that I am insufficient. Outside substantiation goes a long way, but I don't necessarily wait for it. Similarly, I am usually my first target for my anger. I am trying to manage my condition -- you are very right about that -- but it's an up-and-down struggle. My condition leaves me so tired and confused sometimes, I can't get back on track without help. Without getting back on track, I easily fall into a vicious spiral. (Even now, I've gotten so caught up in getting back to you that I've forgotten breakfast again. And without breakfast, I'm behind in my supplements. Sigh. Better go now.)

Good Luck, I find it surprising that you hubbys mistress is the only way you can find a friend.
I would feel differently about it if you both talked and agreed before she showed up.
Like I said, this is not a triad. Read the book, Opening Up or ethical Slut ... I recommend the first.
You are in a V relationship not a triad. You hubby at the bottom of the V.
I hope the best for you.

Calirn13, funnily enough I have just ordered the book "Opening Up" and it is in the mail. I'm glad to know you recommend it. (I looked at the other, but...) I also ordered "What Love Is".
I know we're in a V. I had thought that a V was one variation of a triad, though obviously I'm still learning the vernacular. Also, since there's not a lot of polyamorous people in this group, I didn't want to add in a unknown term.
Are you also a member of the polyamory support group? You seem quite knowledgeable, and I've appreciated your insights.
Yes, I wish my husband and I had started this differently. So does he. He had, years ago, brought up the subject casually, vaguely and without any confidence, so in a conventional way, I shut down the topic quite easily. Has he been burying something important to him for years then? That's part of why I feel I need to give this a try.
Frankly, I have yet to observe an example of polyamorism that doesn't seem to be a coping mechanism for one or another type of inability to fully open up emotionally. But what if I'm wrong? I really haven't seen much yet. That's why asking questions and researching is so important now. Again, I appreciate your insights and suggestions.