I’m in a mixed relationship myself, although I’m a non-Christian, so this is just my two cents.
Your boyfriend is not responsible for the anti-Catholic sentiments of his family, but he should be willing to stand up for you to them and put a stop to that as needed. If he’s the one making those statements occasionally, it sounds like you two might need to have a sit down talk about boundaries and respect. He might not agree with you, but he should be respectful of your feelings and your beliefs. If he’s preaching bigotry towards Catholics, or anyone else, really, that’s kind of a red flag. You might want to think about whether it’s worth your time and sanity. Personally, if family members and rando parishoners were casting dispersion on my faith, especially to my kids if I had them, I’d tell my boyfriend that he’d better collect his folks or I would.
I guess at the end of the day, you have think about whether compromise is possible without you being the one to do all the compromising and how you feel about dating someone who may think you’re going to hell. Like, in my situation, my boyfriend is so Catholic I swear he bleeds holy water and he would love nothing more than for me to convert, but he would never let anyone talk down to me about my faith or try to put pressure on me.
You have to do what’s best for you and the kiddos. Being single sucks, but it’s better than having to fight with someone about religion or feel left out all the time.