My first thought - this "diagnosis" came from OW once she got pissed off about you moving back in!!!

I rather doubt the diagnosis of BPD in this case. The danger, you see, is that WASs almost all can look like they have BPD or NPD when they are in their crisis - but if they weren't that way before all this, they won't be that way after, either. Personality disorders are constant, lifelong things, so if someone truly has one, you should be able to look back 10 or 20 years and see that their behavior THEN fit the pattern too.

I have no doubt that most WASs ARE suffering from mental illness - but a temporary form, consisting of depression, addiction to the dopamine "high" of the affair, and a curious loss of empathy that goes along with that.

I'm not saying that some WASs don't have NPD or BPD - just that it's really a small proportion, and it's too easy to think they all have it.

My experience with true BPD patients in a medical setting is such that I doubt most spouses of someone with BPD would actually fight to get them back! They are incredibly difficult and annoying to work with. The typical scenario in a doctor's office is that they engage in "splitting". When they first see you, you are the best doctor they ever saw, their savior, so fabulous. Then, before you know it, you are the devil, a horrible person, the cause of all their problems. Borderline sounds like it would be a mild illness, but it's actually quite serious and difficult to treat.

I think your guy is just depressed, selfish, self-absorbed, and commitment-phobic. Only you know whether those are new, temporary traits, or long-term issues. Seems to me that the best thing you could do is encourage him to get appropriate care for his depression, and take good care of his health generally, so he can work and provide child support for your kids. Meanwhile, focus on getting yourself an income that can support you and the kids so you aren't subject to his whims.

BTW - why not ask to attend a therapy session with him, so you can "learn" about this diagnosis?

Are there clues in his distant past that would be consistent with BPD? Multiple episodes of "bestest" friends who then became bitter enemies?

OH - and NPD seems unlikely, because I can't imagine someone with NPD admitting to having a serious mental illness like BPD!
Ellie