How to stop overthinking things in a relationship?

I am sorry you are going through that. It is definitely hard to have to go through and can definitely take a toll on someone and on a relationship. One of the ways I like is to challenge and question your thoughts. Questioning your thoughts using questions like "Is what I am thinking relevant to what's happening", "Are my thoughts based on facts" etc. Questions can help in overthinking. But of course, different things work for different people. So it might and might not work for you. I hope you find whats works for you. Wishing you the best. Good luck.

If you are overthinking something, the best way to stop is communicating. Just ask the other person for the facts.

As they say ignorance is bliss. We are who we are. Look deep into whats causing the problem. Is it just nerves. Or maybe it's not you?

By doing better things in a shorter spam of time so I don't return with my mind back to what happened about the "thing".

You have to trust your partner. Overthinking things will always be part of your life. If you have trust and faith in the relationship then you will be able to stop the overthinking.

Talk to them. Take a minute to think about them things. Ask yourself questions like: What do I want? What am I thinking this? Why do I want this?

Talk to your partner. Every relationship is 50/50, and if you have any concerns, you need to talk about them!

Take some time for yourself. Too much thought about another person can lead to an 'unhealthy' obsession and that is not a good thing, right? Falling into this trap can be easy causing over-dependence, jealousy, and eventually depression. All of the latter states lead to a loss of your 'personal' power and can cause a relationship to deteriorate quickly which kind of defeats the purpose of the whole thing. Therefore it's critical when things reach an uncomfortable level in relation to you concentrating too much on your partner (or anything outside of your self for that matter) that you turn your concentration back onto 'yourself' and what makes you happy and feel satisfied (outside of your relationship).

Its important to understand that both of you are human beings and prone to make mistakes. Both of you have a person life, dreams and aspirations and both of you need to respect that

This is going to sound cheesy but just let things happen when they happen, that means to not analyze every text or conversation, and to enjoy being with the other person. It'll make you both happier in that relationship