He does that to make you insecure so you think you need him. It's a mechanism to allay his own fears of being flawed and lonely. A man who wants to change his girl is just weird! Sounds like he's a prick and you are able to see past and appreciate his better traits. Explains why he is scared to lose you! Don't Walk... Run....
Important (watch in full):
Gaslight (1940 film)
Good Luck!