Bipolar Disorder Support Group
Bipolar disorder is not just a single disorder, but a category of mood disorders marked by periods of abnormally high energy and euphoria, often accompanied by bouts of clinical depression. This is the place to talk about your experience with bipolar disorder, learn from others' experiences, and find support.

I was in an 8 month relationship with a guy and he moved in with me the last month of it and everything seemed perfect. We had fun and talked every day and planned a future. On this past Monday I came home from work and he was just gone, no answers no note no anything just gone. I came to find out later that day he went back to his hometown to be with his ex girlfriend that I never knew about. Luckily for me she tried to help me understand and told me he was bipolar. He never told me that nor have I ever met anyone with this. I am trying so hard to understand it all but I can't process it. No breakup I've ever had didn't have a reason to end except this one. I don't know what to do or think, please help me.
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Hey All...I hope that you have a lovely, peaceful beginning of your weekI have a bunch of chores that need doing but may put them off til tomorrow and just hang out with my landlord/roomie todayWhat about you?...Anything special going on?Have a great day and take good care of you!!..Xo
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Once again I've had a fever today. I'm not going to the hospital because that's a huge waste of time but I did schedule a dr appointment for Wednesday afternoon.

Hope all the broken pieces come together for you
Again, big hugs
As I've seen on other forums lots of ex's believe/say their partners are bipolar, asperger's, sociopaths etc - but that's just their attempt at explaining why the relationship broke down. So when his ex told you he was bipolar then unless he was diagnosed and actually told you I'd take it with a pinch of salt. Especially as it seems from what you said she is the one he's gone back to.
If he's gone he's gone and I suggest you don't try and attempt to analyse but move on.
Probably the divorce and breakup board would be more appropriate
https://www.dailystrength.org/group/breakups-divorce
If you really are set on understanding more about bipolar there is a long thread on bipolar for partners etc on the families & friends of bipolar board
https://www.dailystrength.org/group/family-friends-of-bipolar
Whatever, he started a relationship and now it's ended - unfortunately you don't have to be bipolar to be deceitful, unfaithful or lead people up the garden path.
I really don't think there is much we can offer to you, some bipolar people act like this, others don't, some people without bipolar do this and again some don't. To be honest, it's less of a bipolar thing, more of a guy thing.
You aren't really going to be able to resolve this, people have their many and various reasons for going and they, and others around them generally tend to be less than honest when it comes to reasons. I've been on the receiving end of break up after 9 years (no they weren't bipolar),
Get some support for your own personal issue - the pain of break up - the link I gave for the breakup and divorce board is best.
Ok, but what do you expect to get out of this? What is the knowledge/ understanding you are looking for?
You said you aren't particularly bothered about the breakup - so maybe just let it go?
From what you have said it sounds like he left a girlfriend and children to be with you - and has now changed his mind and gone back to them. Sometimes guys do this and sometimes people in the middle of a bipolar episode go off - and then when their episode wears off they return to their previous partners. That while in an episode they do things they usually don't. So in a sense the reason why he's gone is because he's come back to reality.
That seems to be a very unpalatable possibility for you which is one reason why I've tried to steer you away from that.
Having said that, if you are getting information about him from the woman who from her perspective he cheated on with you - maybe she's just saying he's bipolar so you will let it go? So you won't attempt to get him back?
Bottom line, he deserted a girlfriend and children to be with you and then deserted you to go back to them. Do you feel you need to understand that further - something is clearly up with him and it looks as if you got a lucky escape
This board is for people with everyday challenges of being bipolar and I can't figure out what you are looking for from us? All I've given is just conjecture - we don't know him, we don't all do the same thing and the person who has told you he is bipolar has some possible motives for not being truthful.
I know it sounds stupid to trust his ex now current girlfriend but she isn't saying it out of jealousy or to keep me away from him and she's helped me understand more than I would have if she didn't tell me what happened because he just blocked me.
I get it's easy to tell someone to let it go and get over it and I did care about him more than I can explain and I still do. I don't need advice to cope with a breakup I just was looking for help from anyone. Never meant to come off as offensive or offend anyone and I'm sorry I asked for help in the wrong place.
DS is a really good site and the Breakups board or Healthy Relationships board here are really good
I'm really sorry that you've been hurt.... Big hug.....xo