Can't cum?

So my boyfriend and I have been together for a year and I just.. haven't cum by him. like ever. we've had sex loads of times and he's eaten me out a lot. but nothing. I mean I've gotten close! but when I feel like it's gonna happen it kinda sizzles and fades out!! I always feel really bad and pretend to cum..
over the time we've been together it's just become a chore to have sex. I LOVE HIM! I love being around him and still find him attractive, but I know I'm not gonna cum and it's just not gonna be as fun anymore. he's started to notice and idk what to do! 
suggestions?