Abusive ex

Hi just wanting some advice. I was previously in an abusive relationship. He occasionally hit me, kicked me, spat on me, choked me out, ripped my hair out ect. he cheated on me by making fake accounts and messaging other girls. When we were splitting up he said that no one would ever want to be with me because I’m too difficult. I know that my abuse was nowhere near as bad as other women have been through, and completely understand this. I am now in a new relationship and have been for 6 months. He is absolutely amazing and would never lay a finger on me. Completely caring and supportive and mature. However, I occasionally start arguments because I feel like he’s going to leave and could do better than me, because like I say my ex said no one would ever want me. I sometimes think he could be cheating by making fake account, even though he constantly reassures me and offers me to look at his phone to make me feel better. I just wanted some advice on how I can stop feeling this way