Catholic raised here as well.
When my mom uses the analogy "Why buy the cow when you get the milk for free", I told her I'm not a fucking cow. And I'm not stupid enough to be with a man that ONLY wants me for sex!
It's insulting to both sexes to think that the only reason a man would be interested in a woman is for sex/her virginity. My husband and I had sex before marriage. He didn't give a shit I wasn't a virgin. (He was also raised Catholic) He valued me for a host of reasons, none of which had to do with my 'purity'.
At some point you just have to let it go. I moved across the country from my parents, my father didn't talk to me for 2 years. They eventually got over it when they realized I wasn't going to come crawling back. If they wanted to be in my life, it would be on my terms.
There is no making your mother happy. And frankly, she sounds like an emotional terrorist, lol. Don't feel guilty, you sound like you have a great head on your shoulders. Continue to do what's best for you.