I don't see your situation as all that unusual. I mean we all have our limits. Even people with very active sex lives don't always like talking about things in detail.

There are asexual people who aren't celibate and you're already involving yourself in this sort of discussion up to a point - so i would lay off on pressurizing yourself. You are who you are. Maybe let some of your closer friends know so that if you have to excuse yourself from the conversation after a certain point they'll understand.