Biggest realization I've ever had

I just got done listening to a few recording I had, which I don't want to get into.
I know he cheats, but at the same I feel like I don't have enough solid evidence to prove it and with that I have too much doubt to confront him with full confidence and conviction.
I was told recently by a temp therapist that my problem is I doubt myself too much. Since then I've been really trying to focus on figuring out why and where it comes from.
My recordings have slowly come together and even though I haven't finished putting all the pieces of the puzzle together and it still leaves him plenty of room for denial..... as of a few minutes ago I know now that I don't need to put the rest of it together. I will never have absolute proof that he won't argue with.
What I figured out is my "doubt" is the missing piece. It didn't come from childhood trauma or abusive past relationships or anything like that.

I put it there myself because it protected me from the truth that I wasn't ready to face.