Dear LW: You know how they say that one should never be a cheater's mistress, because once he leaves his previous relationship he will cheat on you too? Your boyfriend gave you a glimpse of his sense of compassion, or rather, the void where it should be. Aside of moral and ethical considerations (of which there are soooo many), consider the practical one that one day he's going to turn this attitude on you.

Dear LW's father: you handled that malarkey with grace. I am impressed, sir.

Dear boyfriend: I'm not going to argue with you about your asinine beliefs, but simply as a matter of practicality, consider apologizing for the sake of not keeping your girlfriend in the middle of a fight. TBH, she should have dumped you because you are a bigoted jerk, but since for some reason she hasn't, mend fences and just say "I am sorry". You can swallow a little pride for the sake of someone you allegedly love, assuming you're capable of it.