I don't know what to do

I live with my bf of 3yrs. We have animals together, and want to get married, and I truly love him. He would do anything and everything for me.... But he has no sex drive. This had been our only real issue, I'm always horny were as he is never. I haven't had sex in 3 weeks. When we do have sex I have to start us off and it's fine, we both have a great time. But I can't always start things off, I want to feel wanted. I don't know what to do, I'm at a breaking point, but he's the best guy I have ever been with