"I don't deserve you at all"

"I don't deserve this at all"

"I don't know how I managed to trick you into thinking I deserve you"

"You're perfect you deserve so much better"

"You're a way better boyfriend than I deserve"

"You're too good for me"

"I feel like you deserve someone better"

"I wish I was the girlfriend you deserve"

Or any other variant. Is this just a low self-esteem thing? I've always been sure to give her a lot of attention and do a lot of nice things for her in hopes that it'd get better, but these phrases continue to slip.