Roommate gives me a hard time

Another thing I dislike about my roommate is how he constantly tries to give me food.  I understand that he's being nice and doesn't now how many issues I have with my eating habits, but I tell him no and he cooks only the greasiest food, so I can't even have a little.  And he seems to give me a hard time now that he knows I don't like real sugar.  I prefer the taste of aspartame because 1) I have eating problems and 2) I started on diet sodas when I was young, so real soda tastes like syrup.  Whenever anyone offers me a soda, or juice, or anything with sugar or calories, I say no thank you, and he mocks me for not liking sugar.  He won't even be part of the conversation, he'll be sitting at his computer with his headphones on and if he catches part of a conversation about it, he starts mocking me.
Another thing is that I tend to have this one girl come over to cook with me or to jog once in a while, and it was cute at first to tease me about it, but he's moved from teasing me to claiming I'm a terrible person because I won't have sex with her.  He's like "you make her come over, and she wants it, then you just send her on her way, that's probably making her feel terrible, you're a terrible human being for making that poor girl feel so sad." Omg, I didn't even do anything, is it so wrong to have a friend that's a girl and not have sex with her?  It's like some strange backwards world in his head.
These are the two day to day topics he brings up.  He mentions that I eat super healthy and mocks me for that, and he mentions that I lead on girls and that it would be better to do a one night stand type thing with her than to just be friends.  The end of the week can't come soon enough.