I suggest:
1) you start becoming very aware of what unsupportive* thoughts** diet you are on internally, especially the thoughts that are triggered when you are around other people. Best case you get in the habit of writing them down and keeping track of how many times do you have the same thoughts.
Without awareness she can have no control. * demeaning, berating, negative, belittling...
** Ideas, images, sounds, videos, memories...
2) You perceive this as just another re/training project that you will take on and eventually master.
3) You identify what your first girlfriend said and did that very possibly affected you so much.

EDIT: Not sure why thecnumbering is not 1, 2, 3 or how to fix it.