I need to stop being reactive to things... like for example, if my partner says something that kind of rubs me the wrong way, and it's not really a big deal, how do I just STOP myself from immediately reacting negatively to it? 

This is causing such a breakdown in my relationship, with my constantly reacting to little things that shouldn't be a big deal, and I really really need to stop. When I am in the moment, it happens so fast and before I can even think about it, I'm reacting or crying. 

I just want to be fucking mellow and not react to every damn thing. 

I don't know how. I can't get into therapy for several months (I'm on a waiting list for assistance with Healthcare and behavioral health) but I don't know if my relationship can handle several more months of this struggle.