The key here is, a man wants to be a woman's first (and only), particularly if he wants commitment.
A women is often secretly pleased if a man has a past: it proves he's not a loser and that feeds her ego that she "beat out the other women" for him. ("He may have slept with them, but he's with *me* now.")
If a guy has an affair, say, what happens when the woman finds out?
She screams, "Roger, how *COULD* you?"
(A woman in fact is FAR more threatened by her man becoming emotionally close to another woman, than by a one-night-stand, though the one-night-stand is actual explicit sin.)
But if a woman has an affair, the man doesn't ask for an explanation. He *knows* it's over.
Seriously?
There's the sexually transmitted disease issue. Objective fact.
Marriage is to be held in honor among all, and the marriage bed is to be undefiled; for fornicators and adulterers God will judge.
Hebrews 13:4, New American Standard Bible (NASB)