Namasate, I think irregardless, this is going to permantly change the nature your relationship with her. You're not being overly sensitive. She is your "best friend" with that comes a certain amount of expectation regarding maturity and morality.
What would I do? I wouldn't necessarily end the friendship, but I would be honest with her about my feelings. I have a friend like this. We were close like sisters and then she started dating a married man. I told her how I felt about it and there were a few years where are relationship was strained. Now she see things the same way I do. She admits she made some serious mistakes and we have rebuilt the friendship we had and it is much more mature and honest.

Thank you. That is my fear..she is a sister to me, and I know this changes my perspective on our close relationship, and that saddens me. I dont want to judge her or tell her she is making a mistake...that is her business, not mine. I know I need to put the focus back on me. It just hurts to know that my world got a whole lot smaller with this one.

Truthfully, Im shocked right now.

i understand how you are feeling and that is normal.... we, victims of high treason, are forever bound to have trust issues, and it takes time to heal that.
my "best friend" who initially supported me when he left me, is now not speaking to me and "staying out of it", as her husband is my ex-best friend and "she doesnt want to take sides"
that HURTS.

"You're not being overly sensitive. She is your "best friend" with that comes a certain amount of expectation regarding maturity and morality."

Considering what you've been through and her seeing first hand the damage a home-wrecker can do.... then deciding its okay for ME to do it.... Narcissistic? Selfish?

I'd have an issue with this if I was in your shoes. I don't think you are overreacting at all. I wouldn't say don't be her friend anymore, but I personally would limit my contact with such a person.

I do not believe you are being over sensitive, and I also believe (do not know your age), there will be more of these scenarios in the future.
Not saying you will have more friends choose infidelity over commitment, just similar circumstances.

15 yrs ago, a friend, or what I felt was a friend, had the picture perfect marriage, loving wife, and 2 adorable kids. He often joked around about "messing around on his wife". 8 yrs later he was commenting about how he saw a girl he would trade, well you know what we men say, to be with. It was my daughter, a friendship ended with a very heated confrontation. 4 yrs later he had an affair, with none other than his MIL. He remains married to his wife/ romantically linked step-daughter, and has moved to another state away from his MIL. Talk about a precarious Thanksgiving. I guess the point is, and I am trying to shed a little humor, as I know this is a difficult situation to deal with. The Dark Side is very powerful, can swoop in and destroy every thing or belief we ever hold.

Being guarded can be mislabeled as paranoia, but better to be paranoid than trying to remove a knife in the back. JMO

is this your best friend?

Yes, my absolute best friend. And also the person who quite literally saved my life in a moment of violence from my ex husband. Now I feel the need to keep some distance.

It's all in your prospective, when I was a in college there was an attractive woman 20 years older than me that worked in the post office at the campus, she was married, she and I had an affair for months, I actually met her husband on a few occasions, I left school and never saw her again, didn't think much of it.

My wife of 10 years left me for a guy she was having an affair with, I wanted to kill him lol, shoe was on the other foot so to speak, I hadn't seen that side of it before. It is all in how it is percieved from experience. She may not be trying hurt your trust, she may not see as much wrong in it as you do at this point, but she may find out one day.

i don't think that you are being judgmental at all. you are being discerning. there is a big difference.

OK< well might not be what you want to hear but if it were me...

and considering this is your very best friend....

-she's already proven how much she values and loves you
-you've already had your moment of proving how your judgment can lapse (you married the guy)

so I'd call it a draw really

she hasn't done anything to hurt you
she may be hurting some strange wife somewhere
but she is hurting herself right now driven with the feeling she is getting her share of pleasure,excitement, fun
judge her based on who she is to YOU
not who she is to others
especially since you already know what its like to make a mistake about a guy

this may just be her period of insanity
and you will be the person she comes to, when she "comes to"
if yanno what I mean

now, if she was flirting with your man
I'd have something different to say
but she stuck with you through your crazy times
I imagine her crazy times are comin down the pyke

hunny I have walked away from plenty of friendships during and since my last relationship, but best friends are a whole different ballgame

there are reasons to dump bestfriends
but I don't think this is one of them

disagree with their choices
be upset with their lack of ethics
but unless that lack of ethics comes a knockin at your door
you may be the best person to help her at some point

loving detachment
its not your life she is screwin with
its her own

ok, off my soapbox

p.s. I thank gawd my 2 best gf's were there for me when I was caught up with my exS and at a few points, had my ethics slip through my fingers , they helped me find my way back to normal again

You ARE NOT being judgmental. In fact I think you're being a friend and should maybe say something to her about HOW YOU FEEL. She could be a victim and being fed a story...or she could need a perspective and realize what a dangerous and selfish game she is playing.

I tend to agree with Joyride. I would give the friendship some space and time, but not to just walk away. I think we have all made mistakes, we have all done something immoral at some point or other--well speaking for myself I have. I want to be forgiven when I make a mistake.

Loving detachment and space will sort out your confusion. What she is doing may not be right, but ending a close best friendship? Not sure about that one.

It would change the relationship for me.

I wouldn't cut them out completely, but well....

I guess what I'm saying is that you're not alone in your feelings.

Cheating hurts SO many people....sigh.

I think that I am sensitve in this way as well. I find I am sensitive to many things that are just to close to home for me. My ex was violent and hearing about that kind of stuff always bothers me.
I am big on carefully saying what needs to be said. You say she is like a sister to you. Do you think its possible that she might understand how you feel if you expressed this to her? That its too close to your heart for you to have an open mind about this? I think there is a way that you could remove these converstions from your friendship and still keep your friend.

Well, you have some good advice here and it sounds like a lot to think about.

I understand how you feel. I had met a married man last summer, but there was no way I would enter into a relationship with him as I know how it feels to be hurt and betrayed.

I have also had a best friend tell me that she could not support me when I remained in a relationship with my ex that was "less then healthy". It hurt to have her turn her back on me because of something that she did not like.

My advice would be the same as Joyride's. Be there for your friend. You can let her know that you do not agree with her choices, but to throw away a best friend is not an easy decision.

Also, I would imagine there is going to be a time when she will need you. Hugs.