How do I handle relationship anxiety?

I’ve been with my boyfriend for almost two years and he’s my first serious relationship. And I’ve been with him for so long that I guess in my mind I’m like “something should have gone wrong by now” and I keep getting scared because the longer we’re together than the bigger the hit if something does happen. I keep thinking he deserves better and that I’m an awful girlfriend and I’m worried he’ll leave me like everyone else does and I feel bad because I’m always talking to him about it and I feel like when I’m like that it stresses him out or that he’s getting sick of it even though he says he’s here for me, he’s never gonna leave, and that he doesn’t mind it and just wants to help me through it. Is there any tips I can get to manage it better and make it easier to deal with my anxiety?