Would it be OK to grill my SO about his sexual past. I want to make sure he hasn't done anything I disapprove of.
Do you really think it's that important to know about what happened in his past?
Well, I'm also just curious about the kinds of things he's done.
It is okay to be curious about someone but It wrong to pry into other people's private business. Especially wanting to know their sexual past so you can judge them about it.
I figure if he's done nothing bad, he shouldn't have a problem telling me about it.
Honestly, if he's done something he thinks you'd be ashamed of, he wouldn't likely tell you anyway. Accepting him for who he is now is going to make a stronger relationship in the end.