Anxiety and trust

I have always struggled with opening myself up to relationships but recently made the step with a really nice lad who I can see a positive future with. I’m really struggling with trusting him as I’ve always been the bit on the side or not good enough for someone. I worry I’m pushing him away by worrying about the trust issues and can’t stop my mind thinking the worst all the time.

I’ve been cheated on and had someone I was in love with take their life in the past and struggle with that a lot.

I need advice on how I can stop my mind going into overdrive and ruining something that could be really good.