Seeking expert testimony is a sign of strength. A personal relationship with a caring professional is proven clinically effective.
I believe that I can help you with this question.
Your boyfriend seems to have some serious sexual issues that may stem from his childhood.
His reactions to sex, his previous attachment to prone sex, and his seeming revulsion or disinterest in sex or touching is a clue to me that he have be suffering from Asperger's Disorder, a mild form of highly functional Autistic Spectrum Disorder.
This would be my first line of inquiry.
Does he have trouble making eye contact with others? Was he a late developer in socializing? Is he sometimes awkward in his posture, or socially awkward?
Does he seem to have a fixation on parts of things? He has a negative fixation on vaginas and things "oral" including kissing and oral sex.
I strongly recommend that you make an appointment to see a sex therapist, who is a mental health professional with additional training and national certification in sexual matters, and would be the best one to make a face to face assessment.
He or she should understand the particular sexual needs and quirks of someone with Asperger's, if this is the case, or with general problems as your boyfriend seems to have.
The best way to find a nationally certified therapist is at this sight:AASECT
I wish you great success in getting this sorted out. He has responded positively before, and now you need to dig deeper and see what further treatment is needed.
Elliott, MAE, LPCC, NCC, CCMHC