I'm a terrible overthinker how do I stop?!

I've just started seeing this new guy who is lovely but old insecurities and worries are starting to crop up because of guys I've seen in the past. They've either lost interest or they try and play games or choose someone else over me. And I don't wanna put me old overthinking issues on him. Is there anyway I can stop? I really hate it, I like this guy and wanna see if it goes anywhere but I also don't wanna keep worrying like this. I find during work my mind is taken off of it and I focus on studying helps but when my mind starts going down the rabbit hole it makes me feel like shit 😅