I don't understand why I simply can't let go. It's been a good 6 months since we broke up and I am with someone else, but my ex can't seem to leave my mind. He's in jail right now its been 1 week and a couple days and before he left he felt the need to tell me he didn't hate me, but he didn't care about me anymore. It kind of hurt to hear that but hey, I'd be salty too if he left me for somebody else... my mind is racing over this and I really want him to know I still care. I know I'm so wrong for this. What do I do?

(P.s My ex and I were together for 4 years...)