Hi there! I can relate to this so much! I used to constantly overthink any interaction I had with someone and pick it apart until I'd come to some warped conclusion that I had done something wrong or they were "mad at me". It didn't matter how close I was to the person, even if I trusted them with my life I would never truly believe them if they were trying to reassure me that nothing is wrong and that they love me exactly how I am. It is exhausting living with a brain that assumes the worst-case scenario - not only for you but for those around you who have to convince you time and time again that everything's ok.
I found what helped me was to be really open and honest about how I was feeling, obviously this can be really hard to do initially but the people who truly care about you will appreciate the dialogue and it will help you to ease yourself off "the ledge" so to speak. There are so many mental health conditions that come with crippling anxiety and put us into a "fight or flight" state - which makes it near impossible to think clearly in that moment. Taking some time away from the situation/circumstance is so beneficial in processing your emotions and preventing the "overreacting" that you mention. I personally can't think straight when I am in an anxious state, so if I feel myself going into that I will set a boundary with that person and say something along the lines of "I would really like to hear what you have to say, but at this moment in time I am feeling quite *insert feeling here* and need some time to process your words. Would it be ok if we came back to this conversation a little later, as I would like to give you the respect of an appropriate response, but need to think about it for a little while so I can respond appropriately?". Boundaries are so important to set for yourself, otherwise you are doing yourself a disservice by discussing/acting on a situation when you are in a frenzied state.
I find its helpful to (in the time you take to process) speak your feelings out loud to yourself - acknowledge them rather than try to squash them down - and ask yourself what has happened to make you feel this way. It works well in situations when you feel incredibly anxious or emotionally dysregulated as you can ask yourself questions like "ok so I feel *insert feeling here*, what has changed in the last X minutes to make me feel this way?". This gives you an opportunity to slow things down, acknowledge your feelings, and remind yourself that it is ok to feel how you are feeling - but feelings/thoughts are not facts and you don't have to act on them. This might help you break the thought process before it escalates and spirals into a dark or hard place, and will prevent you doing or saying something you don't mean and may come to regret - which will only continue the harmful overthinking/over reacting cycle.
If you're honest with those around you, set some boundaries for yourself to help you cope/manage your emotions better (and allow others to do the same), you will begin to become less reactionary and will deepen the relationships with those around you - rather than pushing them away.
Hope this helps!
