how to brush off overthinking?

i’ve had the worst flare up these past few days, mainly around my relationship and my insecurities. i’m more than familiar with intrusive thoughts surrounding things i care about most, but usually reassurance would help. however, it can get exhausting quickly and i’ve heard it‘s just not the best method. any advice is appreciated !! i’m more so just looking for ways to not self sabotage or lose sleep from the anxiety.