That is the worst attempt at an analogy I've ever seen:
A) It isn't a crime for her to cheat. Also, nothing is being "stolen" from her boyfriend. B) Even if her action is immoral, it is not my responsibility to play morality police. She's an adult and can make her own decisions. C) My participation is not through omission.
I have posted an accurate analogy elsewhere in this thread, but let's fix yours. My neighbour's GF knocks on my door and offers me her antique table. I know it was given to her by my neighbour's late mother, but it's a lovely table so I accept it. Her bf (my neighbour) gets mad because he loved that table. You live three streets over and knock on my door to tell me I'm a piece of shit for accepting the table.
Here's why this is more appropriate:
A) She owns the table, it was given to her and it is hers and hers alone to give. Just like her sexuality: no woman is owned by her partner. You've brazenly likened the woman's sexuality to goods owned by her SO.
B) My neighbour's involvement is an emotional investment into the table. For all I know, he may have stubbed his toe on the table and recently feels like he could use more storage space instead. In the same way, I don't know if some of these people are on the rocks or not: and it's not my responsibility to sort it out.
C) Following this, it is clear that my participation is incidental. I was offered freely offered something and accepted it. The fallout of losing the table is between my neighbour and his GF and has nothing to do with me as I did not solicit the exchange. I've never said anywhere here that I've worked to undermine someone's relationship to sleep with a partner. That would be unethical. In any case, the GF in my analogy was going to go knocking on every door down the street until someone took the table anyways. But I'm a monster? GTFO of here.
I go to bars and hookup with people that sometimes are in relationships. You want to screen everyone to make sure they're following the bible? That's your problem.
Stop treating women like they're children and assuming men own them.