Self esteem issues

Why? This is what I ask myself after a thought of my husband cheating pops into my head. Why do I think these things. My husband has never given me a reason to not trust him. I have been cheated on almost every relationship I have ever had other than this one. I finally found someone who is a decent person and I'm constantly afraid. I don't want to push him away but I feel like I am. Someone please tell me I am not alone.