My girlfriend tells another guy she loves him, but not me?

This other guy she used to flirt and arrange meets with before we were together. He wont lay off her. I know she likes him as a friend and has described him as being funny before. In the past I have told her that I love her and she went on to say how she thinks love is complicated and stupid, yet I read her chat with this guy and he said that he loved her, she replied straight away saying she loved him back. Im worried that she doesn't like me and would prefer to be with him, also of what he may think as he is a dodgy character. Any help is great asap guys, thanks.. guy.