I'm friends with my ex, but I'm dating someone else

Just as the title says, I am still friends with my ex-boyfriend and now I am dating someone else. I stayed friends with my ex after we broke up holding on to hope that we would get back together. Indeed, he had some hope that that would happen; however, I think he knew that I could find someone else. The last time he asked me about dating him again was three years ago, I told him I wasn't interested. He hasn't asked me since then and we have stayed friends. I will say that last fall he told me about a woman he was dating, indicating that he was hesitant to tell me at first. I was fine with it. In fact, I felt relieved that he told me because I was worried he was still hung up on me. Unfortunately, his new relationship did not work out. Now, I feel like the situation has reversed: I am seeing someone else, and I am hesitant to tell my ex-boyfriend about this, even though he is sure to know about it eventually. I'm not sure if I want to tell him over text message (like he did with me about his girlfriend, which I really didn't mind), or tell him over the phone or in person. Knowing that he told me about his girlfriend when they started dating, I think he'll handle the news well enough. I still feel uneasy about this.