I just found out my girlfriend of many years has been having an affair for 4 months with someone she met at a bar. She has unregulated, poorly and inconsistently medicated BP which she still struggles to accept and undermines/self-medicates with alcohol. She is getting worse not better as she gets older. Her job was in jeaopardy during these past for months, as she has chosen partying and cheating, apparently, over her career. I am devastated by the realities I am facing currently re: her recent behavior, specifically due to the fact that it's not a random one night stand, but a 4 month affair. She denies it but I have enough evidence to know she has been lying to me for months. I understand BP may have made her go to bars/cross lines with impusivity, etc. - but I don't understand what BP has to do with lying to someone she says she loves more than anything (me). She has not seemed manic x the past 4 months, so how can this betrayal be legitimately attributed to BP? When I look back at texts, etc. I can see the premeditated nature of this, the planning literally that has gone into avoiding me and creating space for her to get her drink and God only knows what else on...Please advise...I appreciate all perspectives and am grateful for any insights offered.

I forgot to mention that she has experienced severe episodes of depression during these four months as well...she is totally out of control at this point as far as I can tell, no shows for counseling appts, has given up on meds/med combinations, stating they don't work etc...alcohol has been an issue. She told me when I found about this person she has gone to bars alone because she just "gets this strong desire to go out and have an exciting/amazing time" etc.."...but she has not taken me with her, of course. This is relatively new...or at least the betrayal/affair part. I'm just struggling to determine how much of this madness I can attribute to her unregulated BP, and how much is just betrayal/lying. We are currently broken up and not speaking despite her daily texts to tell me she misses me. All of it breaks my heart, but after years of being supportive, I've hit a wall with this one.