I understand how you feel, I had similar problems which also ruined relationships :/ irrational thoughts are such a hard thing to cope with, although I think there is nearly always a kernel of truth to them so you shouldn't beat yourself up over having the thoughts. I remember it getting really frustrating though because I could never communicate the legitimate part of my concerns because of how I reacted to them.
When im able to focus enough I find that writing down my thoughts first before I speak them really helps me rationalise things, but sometimes im just way too caught up in my thoughts to remember to do that.
Hopefully you can start to gain some more control soon, therapists always help even if its just to have a rant to get everything out of your mind (: best of luck