Can somebody please explain

So my boyfriend has this thing about small skinny girls (no I’m not hating on y’all, you’re all beautiful) he always looks at them on Instagram and stuff. He also watches porn which I don’t really care about bc usually it’s the act of sex and not the people. I tried to have a conversation with him about it and he said that he doesn’t look at them the way he looks at me. Like he wouldn’t want to marry somebody like that.. idk can somebody explain 😂 he said he doesn’t mean that I’m not beautiful or anything he just didn’t know how to explain it.