Ex Problems 😕😕

Okay kinda long but I really need advice!! So my ex and I broke up in 2014. He was my first, however he ended it after 3 months to get back with his ex. Fast forward to this day, I’m dating one of his (used to be) really good friends. Anyway, 2 months ago he started snap chatting me and we met up just to catch up and see how each other was doing. However, he got upset when he found out I’m still dating his friend. He said I’m a liar and now won’t talk to me at all. I thought we could be friends because I want him in my life. WHAT do I do?!