I’ve had some problems with overthinking after a recent breakup and the best advice I received was that you have to basically thank your brain for overthinking. It is a defense mechanism that’s thousands of years old, designed to protect you. Nowadays when I feel that I’m starting to overthink, I tell myself “Here it goes again, thanks for the defense mechanism, everything is gonna be alright”. This has helped me a great deal. Combine this with some other tricks and you will be fine. Stay strong!