Wow--your BF's story sounds a lot like my H's. He, too, didn't seem to grieve, just went into a wierd sort of apathy. It was as though there was a glass barrier between us that I just couldn't penetrate. After a few months he went into the "Anger" stage, and was constantly angry about everything (including about aches and pains that suddenly attacked him all over). But in between bouts he'd claim he was perfectly happy with our life together ... until he started taking every excuse possible to be sent through work to another city. There, of course, he met his EA at work.
I know it's hard not to take the OP personally--like, what's she got that I haven't? How can he do certain things with her that he refuses to do with me? Why can't he see her (pretty glaring) faults? I certainly spent a long time in all that. But, looking back, H had become dead inside, from all the grief and unexpressed emotions he was hiding from, and all he was looking for was someone that would make him feel alive again.
In H's case, the OW was partly a replay of how he never felt good enough for his mother (OW rejected him as a BF, but also refused to let go of him as her "BMF"), and also, there was so much drama in her life that he could focus on helping her, and advising her and comforting her and take refuge from his own life by obsessing about hers. My feeling is that he didn't entirely see her for who she was, but projected onto her all the qualities he wanted her to have. (And ignored all the dysfunctions--they could all be blamed on external circumstances.)
Yes, H did come back from his MLC. About 4 years after his mother's death, he said he wanted to work on our marriage. It was at least another 6 months before he was really himself (actually, a new & improved more confident self) again. However, without good counselling (primarily before he exited the tunnel) it would have been considerably longer, I believe.
I suspect your BF has quite a way to go, still, and several years of MLC ahead of him. Whether or not he finds the strength to face himself is completely outside your control, though. Take the time for yourself, if you can.
