Broke A Heart

After my first ex-boyfriend broke up with me, I was going to try to be on my own for awhile but I met someone really nice and slept with him.  But I shouldn't have because I realize now for sure that I was never in love with him, and he was really into me and I led him on because I wasn't sure how I was supposed to feel.  I recently broke up with him when I realized that I don't feel about him the way he feels about me, and now I have a girlfriend who I care for a lot and feel more close with than I ever felt with him and it just makes me so confused.  He asked me how I could move on so fast when we've been together for 2 years, and I just don't know why, I just feel this way.  I never thought I'd be the one to break somebody's heart. Usually I'm on the other side.