My ex wants me back after 3 years?

So confused by my ex bf. He has been trying to get back with me saying he loves me and we should get back together. I started dating someone new and now he sees I'm happy with someone else. We were high school sweethearts so we dated for 6 years he was my first love but when we broke up he said he didn't want to get married because we were young and I was the only girl he was with so he wanted to exprenice what it would be like with other girls? So now 3 years later he wants me back? Have no idea what to do? My current bf has no idea that my ex is talking to me agian I really think I love my current bf but I have history with my ex. What should I do?