sex help?!

I have been with my fiancé for 4 years. Him and I don't always have the best sex and the years go by and it just gets worse. He has no clue what he's doing. I love him so much but when him and I have sex it's the most uncomfortable and I can never get aroused with him. He does weird things like the way he talks to me before hand like a boy who just learned about sex and he knows I don't like it. We rarely have sex and I feel bad. I'm not sure how I can get our sex to be better. There's so many reasons for me not to want to have sex. I want to spend the rest of my life with him but I can't spend the rest of my life not enjoying sex with him. PLEASE HELP! Ant advice would be helpful.