Some men become very bitter with women after a relationship
failure. Some men come out of it learning how to be better men.
Some men get devastated by the failure and end up being the
proverbial jerks.
My feeling is you know what you are supposed to do. However, you
don't want to be viewed as a fair-weather lover, and you want to
let him know you are one who stays by her man. What you should do
and what you want to be are two very contradicting things. No
wonder you are confused.
Your dad detests him - and he has yet to know his situation. When
he finds out eventually, how will your dad feel? I can't think of a
suitable word strong enough to descibe how your dad will feel.
Devastated? Vomit blood?