Eventually I hope to be in a situation where this is a problem for me. I come from a strict Christian background. Divorcing my wife was a big deal, and I recently came out as an atheist to my immediate family. (Extended is another story. I don't see them much so don't see the need to tell them anything.)
I've been living with my parents for the last few months and one day they found out that I'd stayed the previous night at a woman's place, a woman I wasn't really in a relationship with. I confirmed that I'd had sex with her. My parents responded that this was something that we would need to discuss. (Ludicrous! I'm 30!!
Anyways, what I ended up doing was saying, in an email to my dad, that since we had different value systems, we could go one of two ways. Either openness without judgement, or don't ask don't tell. He never mentioned it again.
It's unfortunate, because I really value open honest relationships, but sometimes all you can do is agree not to talk about it.
Good luck with whatever you eventually end up doing.