Thank you for asking about this difficult issue. Coping with someone who has OCD can be very challenging as you may feel the need to keep pace with his or her concerns. But there are a few other things I think are worth bringing to light.
Your lover may be experimenting with a gay relationship and may be bringing his obsessive concerns as an attempt to manage his anxiety and commitment. In other words, the obsessive concerns may be his way of distancing himself. Naturally this is just a guess, but the fact that you have had some difficulty with sustaining intimate relations suggests you may be drawn to someone who has a different, but similar issue with commitment.
See this as an opportunity for you to identify what you want from a relationship and what you need. I would focus on being clear about what is okay, and not okay. If persistent questioning about your past beyond the initial questions is burdensome I would state your feelings about the discomfort. Give your partner the opportunity to voice his concerns, but don’t feel like you have to explain yourself endlessly. You are not likely to be able to satisfy him with endless answers. I wouldn’t focus on trying to correct, explain, or convince him. Instead I would let him know how difficult it is for you to keep coping with his concerns, and that it hurts when he doesn’t return your calls.
This is an opportunity for you to set boundaries and become more proficient at expressing your needs. Since it is likely that both of you are experimenting with intimate relationships, being honest about your feelings is a good place to start.
Wishing you patience and peace,