Not interested?

From when I first met my boyfriend (4 years ago) up until about 1 year ago we had sex quite often and it was always kinky and exciting, (we live have lived together for nearly 2 years now) these days he seems to have no interest in it (he's 20) every time I try turn him on he shuts me down.. And when we do have sex it lasts about 5 minutes. It makes me feel like I'm not good enough for him or he's not attracted to me/sees me in that way anymore. Sex is important to me and he knows that (our relationship is a lot deeper than just sex) I don't know what to do anymore I'm almost in tears about it. I've tried different things or dressing up (or down) for him and hinting it but he just isn't phased by it 😞 what do I do???