Why do I feel so insecure about my relationship?

the last few weeks my boyfriend and I have been fighting a lot. we finally figured everything out and we’re ok again. The only problem now is ME. I seem to have a hard time letting go of all the negative feelings. I want it go back to how it was before, where we were happy and I’M making it impossible because of the negative feelings on my end. The real issue is that I’m still worried that he’ll leave me due to the fights we had. During the few weeks of fighting I was positive that he would break up with me (because I had someone who used to break up with me constantly in the past then beg for me back then fight and break up etc.). So I suppose I’ve been traumatized? I know this is NOT the same relationship at all (the other guy was crazy) so why can’t I just let these negative feelings go before they ruin my relationship and move on to a better and healthier life with my boyfriend? I feel so insecure and know that I’ve become the problem. I want to be able to fully appreciate the love my boyfriend and I share but I have this lingering feeling of insecurity/worry that he’ll end it… and I know if I keep this up he will end it. How to I believe in us? Trust again? Move past these crazy negative feelings?!