Can you just be friends with your ex?

So me and my ex broke up due to working all hours and living on opposite sides of the country. We remained friends for over a year so we talk every few weeks or just when we can . Now I'm in a relationship with someone else and we've been together over a year and he's just realised that the guy I talk to is my ex and he's being really weird about it . I down want to loose either of them . I'm out of ideas now