Don't worry. Maddy is the same. She frequently will have moments where she just feels inadequate. You mention she has cerebral palsy which probably makes her think that any girl is better for you because their normal. People with those kind of conditions can be harsh on themselves.
Hell I used...
An Ex is an Example of what you shouldn't do next time.
I don't know what happened but from these comments she cheated on you. She doesn't deserve you or your trust. And she is likely to cheat again. She is probably using you etc.
Moving on... *Rage Slap*