On my overthinking

I always think that the reason why he left is because I was a coward. But I'm thinking maybe it was because I don't speak what's really on my mind. I always think that being silent will keep me away from arguments and fights. I don't know, I just have that belief. But, it could be both though. Sometimes I'm okay, like "if that's what make him happy then be it", and sometimes I'm like "where did it go wrong? maybe I'm the problem, maybe our circumstances, maybe my fear, maybe I'm not just the right one for him". I just want to overcome this overthinking.