Don't feel like having sex anymore

The past month I haven't wanted to have sex with my boyfriend. The thought of it is just a turn off. I've always had a low libido, but this is different. I told my boyfriend (of 4 years) and he got really upset and asked if I still love him. I do still love him... I think... it's wired! I don't know if it's just a phase or if I'm not attracted to him anymore. Our relationship is about so much more than just sex, but sometimes I feel like he's more of a best friend than boyfriend. I'm not sure what's going on it scares me. I want to wait a couple more months and see if I get over this. Or do you think this is really serious and we should end our relationship now? I hate how much I've hurt him by this!