I would ditch him without batting an eyelid.
I think this quote says it all really, you owe it to him and yourself to get out of the relationship and move on.
I can't really say whether it is or it isn't just about sex.
Maybe he doesn't like giving you oral but doesn't want to make you feel bad?
Maybe he just can't be bothered?
Maybe he just wants sex himself and doesn't worry about you?
Maybe he is nervous about getting it right?
See how many maybe's there are.
Only way to find out the answers is to talk to him.
Like someone on here as said before "If you can't talk about sex then you shouldn't be having it"
(love that saying!)