Is this real or is he messing with my head?

I have this "friend" who I've known for almost 3 years now. We spend a lot of time together. A couple of months ago we took our friendship to the next level and began an intimate relationship. He asked me to keep it between us because he didn't want other people knowing our business. Maybe im being foolish but that doesnt seem right. Although nothing is official, we did decide to not see other people. I found out he was chatting with girls via the internet. When I confronted him, he told me he was just talking and that i shouldnt worry because I was who he was with every night. He is constantly telling me how much he loves me and is always insisting we are soul mates. He says he hasnt taken the relationship past our friendship because of some serious things going on in his life. Every time I try to walk away he breaks down. In is defense, he has change a lot to appease me. I love him but I can't tell if he is serious about his feelings. I don't know what to believe anymore.