Many people are unable to receive love, feel uncomfortable with lovers who treat them well, and feel drawn to lovers who deprive and mistreat them. In order to get to the bottom of your confusion, you need to find out why you want to leave someone who is good to you.
If I had to guess I would say that you aren't used to being treated well. If your first family abused or neglected you, you wouldn't feel at all comfortable with someone who treats you well. Since we are all creatures of habit, familiar pain becomes as cozy as a well worn pair of slippers. This relationship doesn't feel right, I think because the way he treats you is so unfamiliar that it pinches like a new pair of shoes.
Before you jump ship, I would join a therapy group. Examine all the emotionally meaningful aspects of your childhood and you will find that you are feeling afraid to step away from what you know. The group experience will help you to become more comfortable with loving connections, which will help you to be able to embrace the love that your guy offers.