Help? How do I tell him I don't think I'm good for him?

Ellie
We've been together a year and I love him to pieces and think he loves me but I'm always having to apologise for things I've said and how I've acted and I know that I upset him. 
I don't think I'm good for him. He's amazing to me, I mean like a perfect partner but I can't seem to be anywhere close and I feel he can do better than me. 
Any advise/ideas?