Its a pretty tough question to reply. Trust me, its such a question, that there is no right answer, you go this way, you are wrong you go that way you are wrong.
On principle I follow certain things, among them one is I am honestly dishonest. You may laugh at this, but this is truth. I am dishonest in number of ways, but I am honest to accept I am dishonest.
What do I have to do for that? The best thing is to keep calk, not to talk unpleasent issue, not to ask unpleasent issue and not to step into other's privacy. If people honestly respect the other's privacy, he can maintain his own privacy.
Sex before marriage in liberal culture is very much accepted. Its so accepted that if someone is virgin, everyone gets curious on his/her sexual orientation. Sex in conservative culture (if any still officially exists) is the opposite, they dont want to agree on anything in public. Of course you have to keep in mind, in none of these culture no one boast around what they have done and how many and which way, but somewhere its accepted somewhere it is not.
Rather than pushing someone to tell a lie, why not let it go? I personally feel talking on this or sharing this is not required. Someone asking about this also should be stopped. And someone trying to dig the past is a crime. Its better to leave everythiing behind. As I say, past we cant do anything, present we cant do as walking with us, but we can change the future by doing something good today. Lets do that good.
On a final note, I would say, its better to avoid the past sex or love or affair completely except one thing. If someone has a different sexual orientation, he or she should make it clear. Like a gay going to get married on family pressure, he should come out of the closet and say he was gay with gay acts, so heterosexual life might not be active.
A request to Pussycat and other members, ask good questions like this. The question should be so good that if makes you think for hours on what should be the reply. My vote is, respect privacy, share only what is a must to share.