I have read on here and on other recovery sites that many As have trouble with sex and intimacy after quitting their DOC(drug of choice). Honestly, I have to tell you that what your bf is going through sounds close to what I've experienced myself, in me. I am a victim of molestation and sexual assault(at various ages of my life) and I am very disconnected from the sexual side of my body. It's something I'm working on in therapy and on and off through my life, I've had weird physical reactions to sexual advances, being touched in certain places, etc. This may be totally unrelated to your man, but it almost sounds like anxiety related physical symptoms. I, too, said the same thing: I wanted to be close to the boyfriend or spouse(depending on the time in my life) but my physical body would react and it would discourage me. I literally had to have the feeling that I was having an out of body experience to be able to enjoy sex. Over the years the episodes have gotten less and I have adjusted my mind and body in how to handle them, but I still have a lot of work to do on myself to face the shame from the past.
Has he looked into exploring the issue with a therapist? Another story here: my sister's husband cheated on her, gave her an STD while she was pregnant, and all other kinds of crap he put her through. She hasn't been able to eat a real piece of food since March. She subsists on Ensure drinks, 6 of them a day, and is down to 105 pounds. The doctor's did all the physical tests, exploring her esophagus, etc and found nothing. She literally feels like her throat is closing up when she tries to swallow food and the docs now say it's anxiety. Actually, all the doctors say it's anxiety and now that her estranged husband isn't working she doesn't have health insurance to go back to the doctor for any further testing or meds.
Anyway, my point is that trauma can bring about all kinds of physical manifestations in the body and many of them are confusing to US, the ones who are suffering through it as well as to those around us. Of course, this is just my experience and I may be totally off base, LOL, so take what I shared with a grain of salt and hopefully others will come on here with better advice!