Husband wants my sister more

This is my first post, and I'm not really sure how to go about saying this. I'm so angry, and hurt, and just...everything. last year, my husband told me of a fantasy he has. He wants to have a threesome. Ok, most men do. But then he said he wanted to have one with me and my sister. I was instantly offended. it took me months to get to a point where I could even sleep in the same bed with him. I just felt disgusted. But I let him keep his fantasy, I never bashed him for it, and he said that he found me more attractive than her and would always want me more. Well, today, after him turning me down for sex (Which he does often), I told him he wouldn't turn her down. He didn't say anything, and in my hurt, I said that I wasn't stupid or oblivious. He said to what? I said I know that you're attracted to her. Then I asked are you attracted to her more than you're attracted to me? And he said yes. I asked why? He said because she's thin, and his favorite position is when a woman rides him. I'm a big girl. I always have been. But I never thought I looked bad. He even said he married me knowing my size. But it just hurts to know that he finds her more attractive than me. And I guess it hurts to know that I've been on top numerous times and he hasn't enjoyed it I suppose because he has to look at my body. I've always been compared to her by everyone. And yes, she's far more attractive than I am. I guess I was naive for thinking that when you get married, that person is the person you're most attracted to. Obviously I was wrong. I talked to him about it a little. I asked him if he found me attractive at all, and he said he did, but I'm not sure I believe him.But I don't know what to do about it. How do I know that when he's with me, he's really with me, and how do I know that he's even attracted to me at all now? I just feel lost.