Why do I believe I’m a terrible person after I make a mistake?

I 21F have always struggled with my mental health since I was a child. I have PDD (persistent depressive disorder) PTSD and I wonder if I have BPD as well.

Every time i mess up in my relationship or just make a general mistake I immediately self loathe and believe I’m a terrible person and shouldn’t be alive. Like tonight I overreacted over a situation that shouldn’t have even been a problem. I knew that deep down. However I still started an argument and he was able to calm me down but now that I see where I was wrong I feel like a terrible person. I’ve never cheated on him and we’ve been together for 7 months. I’m afraid that he will see me like how I see myself and leave and I definitely have a fear of abandonment. Truthfully this is the first time I’ve ever been in love and I don’t wanna mess that up because of my mistakes. How do I get over this feeling of being a terrible person and just be happy?