Stop waiting for your family to give you permission to make your own decisions. I understand this was the established pattern. Disestablish it. Next time they say he's not good enough for you, say "I'm afraid I'm going to have to decide that for myself. I've heard what you have said, but I'm going to ask you to stop bringing this up. I'm with him because I want to be. I'll stay with him as long as I want to. We're not going to talk any more today about me leaving him. Now we can talk about other things. Or we don't have to talk at all. But the subject of me staying with him or not staying with him is closed." Then close it. If they keep it up, you must physically remove yourself from their presence.

Your boyfriend and your sister don't have to like each other - ever. But they each have to be courteous. That's all you have a right to demand. But you can expect and demand it. Each of them owes you that. Your boyfriend doesn't have to spend lots of time hanging out with your sister. But, now and then, you and he and she will have dinner together. He and she can eat their food and sip their wine and behave themselves. If your sister acts improperly, then you support your bf by finishing the meal and cutting the evening short.

You have your own issue with your bf over where the two of you are going to wind up living. Keep that separate from him and them not liking each other. Even if you and your bf lived one half mile from your sister, that doesn't mean they have to see each other all the time. Actually, if you and he move back to your home town, it would be easier for you to duck out for time with Sis, without dragging him along.

When Sis gets pushy about how she doesn't like your bf, tell her that it's okay for her to not like him. But tell her you expect her to act courteous toward him as you do toward her guy. Say you know your guy isn't perfect, but then neither is hers. Don't get into comparisons. Just say that your bf wouldn't be a good mate for her, but he's what you want for yourself.

Your firm policy has to be that "Wherever my boyfriend isn't welcome is a place I don't want to be either." That doesn't mean he has to go where you go every time you go anywhere. If you love him then when someone insults him, they insult you. Someday you hope to have a child. Would you tolerate someone being mean to your child? Learn to have some righteous anger when someone you love is being mistreated. I expect my bf not to mistreat my sister. If he did, I sure would make him regret it. Same policy toward my sister. If she were not nice to my bf, I would let her know I was very much offended.