I have serious trust issues and it's ruining life and my long term relationship with my boyfriend.

I had another gigantic meltdown today in my relationship, again, after telling my boyfriend it won't happen again. I really believe that it won't happen again when I say it. But it always does. 

I get triggered and then fully believe he is cheating, lying, that he takes me for a fool, I'm all "I'll get to the bottom of this" and engage in "I know the truth" type of self-righteous behavior and statements. I accuse him of horrible things.

He is apparently not cheating. In reality, i find small things that trigger me and I craft enormously detailed stories of his certain betrayal. 

I'm just about willing to throw out the relationship just because I am so fucking exhausted from dealing with my own intrusive, insecure thoughts all the time. I am miserable. But I don't want this. I really don't.