a) yes, listen to your gut. STOP contacting him and refuse contact from him. He is a toxic, abusive person. He brings nothing to your life except torture and pain.
b) Abusers *rarely* change. Right now, he's in a honeymoon phase with his new flavour of the month. Soon enough, she'll become his new plaything/victim.
Heck, you might find HER contacting YOU in a few years, asking if he treated you as bad as he treated her (how do I know? I was babymama #3 to an abuser and I contacted babymama #3 to get some straight answers).
IMO, you ran into your X for a reason. HP was giving you an opportunity to test your boundaries and confirm the knowledge that this person is POISON for you.