If your ex has been with his girlfriend for three months why has he cheated with you four times since he has been with her?
Obviously, he shouldn't be in a relationship. You have an obligation to tell the current girlfriend that he can't be trusted. If he's cheating on HER with YOU, he probably has other's on the line as well. Have you heard of Aids, VD? This isn't the kind of person you want to have a relationship with.
To clarify, we dated for almost two years. She went out with this other guy one day before we broke up (date: Jan. 14; break up: Jan. 15). I only found out three months into their relationship that she cheated on me. She is still with the guy to this day, and I still have strong feelings for the girl.