Always think about my ex when I'm with my new guy

I got out of a toxic relationship a couple of weeks ago and am seeing this new guy who is honestly so good to me. However whenever I'm with him, especially if we start to do stuff I can't help but think about my ex and almost like compare the two. It really pisses me off how he's still affecting me when we're not even together anymore. It could be just because it's similar situations so I'm just getting like déjà vu but idk, has anyone got any advice how to stop?