Not sure what to do.

I don’t know what is wrong with me, ever since September I have not been physically attracted to my boyfriend at all. I don’t like sex anymore it doesn’t feel good at all it’s not enjoyable, I would rather just not do it. I have been with my boyfriend for 3 years (he is my first one) I am 18 going on 19 and I don’t know what’s up with me. I’m getting a little irritated by him and just not feeling it. But I feel so so bad because he is the sweetest person in the world and would do anything for me, no other guy has that type of personality. Not sure if anyone else has felt like this, I feel like it’s just me. He says he will kill himself and his life will be over if I break up with him so I am too scared to ever do that.