My guess is that she started questioning the relationship, and meeting this doctor was either when the doubt began, or it just exacerbated what was already beginning. She probably liked the new found attention, especially in receiving that which was given to her alone.

As for her jealousy regarding your friend and ex-girlfriends...that's her insecurity coming into the picture. She might have been afraid that not only she was uncertain, but maybe you were as well, and the knee-jerk reaction was to become suspicious without reason.

Conjecture isn't really worth much. The only important thing to know is that she was inconsistent, controlling, and hypocritical. Not at all worth your time.