I Don't Want to Break His Heart, But I Might Not Have Much Choice...

So, I'm currently in a relationship with this guy. He's a year younger than me and we've been dating since June. It is my first relationship.
He's very kind and sweet. Seriously, he treats me better than I have any right to expect. He's a gentleman through and through, always trying to open doors for me and carry stuff for me (operative word being trying. I'm far too naturally independent to let him do all that all the time). He is genuinely the nicest person I've ever met, there is simply not a spiteful bone in his body. He says he loves me, and that eventually he wants to marry me. I believe him, too. We both love more or less the same stuff and where we disagree we've always worked around it or compromised. I never feel safer than when I'm with him.

But here's the thing, while emotionally he is everything I could ever want or need in a relationship, I am not physically attracted to him at all, and even on an emotional level, I know that he loves me more than I love him. I thought that once we'd been dating for a while that the deeper more intense feelings would come, but they just haven't. I do care for him very deeply, but it isn't what I feel it should be. As I said, I'm a very independent person and I can't even stand being on the phone with him for too long. I don't particularly enjoy kissing him. We had our first 'proper' kiss last month at a party and I enjoyed it, but mostly I wasn't really thinking about him (I remember thinking "so this is why they call it sucking face... huh" ) once I did start thinking about him in the kiss I didn't really want to be doing it anymore and broke away. In the beginning I thought that I would grow to be more attracted to him and he's been around to my house and we've sort of rolled around on the couch a bit, but that was fun in a very platonic way. I love being held by him, but lately even his smell, which I've always liked, is starting to turn me off. Matters aren't helped by the fact that he has the cleanest mind I've ever come across. He seems almost innocent, and it's been a joke between us that I'm slowly corrupting him. I'll make a dirty joke (cause that's what I'm like) and it'll go right over his head.
All of this together is making me feel guilty about being with him as he's expecting us to continue forever, or at least a good long time. I feel like I'm leading him on, when I can't really stand the thought of being physically intimate with him, and no, it isn't guys in general as I've been very attracted to several guys before and since we've been dating. And now, I find myself thinking of other relationships I could be having, slipping back into a 'single mentality'. I'm thinking I'm going to have to break up with him but he's just such a nice guy I truly don't want to hurt him, but I can't see another way. Urg! I hate the thought of him in pain but I cannot see another way out! Please, help me. :help: