How do you deal with self paranoia and trust issues in relationships?

I have been dating a guy for almost half a year now, and I absolutely adore him. He is amazing, and I couldn't imagine being without him. However, due to the fact that I've been in an abusive relationship and been cheated on in the past, I kind of make assumptions sometimes about him that I probably shouldn't. We had trouble at the beginning of our relationship pertaining to his ex, and ever since I feel like I've been way too protective. I'm so scared he is going to leave me or break my heart, and I sometimes feel like I'm not good enough for him. It's starting to drive a wedge between us, but I feel like I can't help it. How do I control these feelings?