Mom hates my boyfriend?

My boyfriend and I have been dating for a year now. I'm 21 and he's 22. Recently he moved 100 miles away to start his career. It's been hard on us but we've been trying to make it. My mom despises him for reasons I can't explain. When I ask her why she dislikes him, she says she doesn't but actions speak louder than words. Yesterday, when I told her I wanted to go visit him for the day (I have a curfew, and I've never broken curfew since it has been implemented) she blew up and said, "well, why can't his fat ass come down to visit you." He can't come down at the moment as he's trying to save up money until he starts his job. He starts June 6. It's really difficult because I love my mom and want to please her, but she's completely degrading my boyfriend, who has never done anything to her, in front of me. What should I do?