How do I deal with PTSD after a toxic relationship?

I dated this one guy for three years and we had a super toxic relationship. He constantly cheated on me and abused me and made me feel like absolute shit. We broke up 9 months ago. I thought I was completely over it because it wasn’t bothering me anymore so I started dating. I started dating my current boyfriend (who I absolutely love with my entire heart) about 3 months ago and recently I’ve been struggling with bad anxiety and freaking out about my last relationship.

I know that my current boyfriend isn’t the same as my ex so I try not to compare them. I know my current boyfriend would never even dream of cheating on me or even thinking about it. But I still get terrified of it and think I’m not good enough for him.

He understands my situation and he’s always there for me to help work through stuff but I feel bad that I’m still dealing with this. How do I work past the PTSD and focus on him instead of worrying about stuff that has happened in the past? I don’t know where to even start on working on myself.