Feelings

My boyfriend and I have been on and off for awhile. We've been talking/dating since my freshman year and his sophomore year and I'm a junior and he's a senior. We've been through a lot, both lost our virginities, etc. Here's the thing, I think I'm losing interest in him... By his physical looks and I think I'm really messed up for thinking that way. Because I always hear no matter what happens to your boyfriend you'll always love them. But I'm not physically interested in him by looks...it's not pulling me in, his haircuts, his outfits, his teeth are getting kind of yellow. It's just not what I'm attracted to. Have any of you been through this? What do I do? I love him and I want a change but I don't want to be mean. Help!