My ex is dating someone else

I've been dating someone off n on for 2 years now. I've always been with him more then anyone. But one day we stopped talking so we dated other people for a few weeks. I dated this boy nick n I really really liked him but then the "someone" I've been off n on with came back into my life.. I left nick.. It's been like 6 months since I've dated nick and he started dating my best friend like 2 weeks ago.. I'm obsessed with it like I hate them being together! I still like him.. we were talking for a long time even after we ended our relationship. But I'm also afraid that it might just me being jealous.. Am I a bad person because I'm so emotional about this..