Hi new here...ex question

My ex boyfriend and I are still good friends but I'm still not over him. We wanted different things. He moved on to someone else a little while after we broke up. He expects me to still be great friends and hang out with him and his new gf. I have told him I can't bc it hurts and he doesn't understand why bc we're friends. He says his new gf is cool with it bc he told her we're great friends. Not sure I believe that. She doesn't seem threatened but I don't want her to be uncomfortable. Maybe we should both run!