Whenever something makes me insecure or anxious in our relationship and I get the fear of losing my so, I indirectly push him into breaking up with me by showing him how hopeless I am and how terrible some things are (even when they aren’t). I know by now that it is a mechanisms to protect myself. I am so afraid of losing my so that I’d rather get hurt by myself sabotaging it than him doing it out of nowhere for example. He understands my struggles, is very caring and everything I have ever wished for but by pushing him, I make him insecure too of course and it makes our relationship unbelievably unhappy. No matter how often he tells me that he is happy with me and that he wants me and doesn’t have any interest in leaving me, I am not able to believe him even tho I have no reason to doubt that. I really want to stop doing it but in those moments I lose my control and the strategies I use normally don’t help in this case. I really want to do something to make it easier for my partner and myself. 
Any advice? I would be very thankful!