Boyfriend doesn't make me horny?Watch
Has anything changed? Any new medications, contraceptives, diets, ect?
A lot of things can change a woman's sex drive and make her less interested.
I think it's best to weigh out the physical reasons first so you can know whether it's just your attraction to him or if you should be doing something differently
Therefore you need to try and figure out whether your loss of attraction is due to the normal course of a relationship or whether it could be for some other reason (depression, him changing, health issues etc.).
You could switch it up a little. As in change the way you have sex. Try out more positions (e.g. having you on top of him), introduce some sex toys, have sex in different locations, or play some sexy games to get you in the mood. This sounds so TMI but that's what I would do to try and find a solution to your problem.