Should I tell my boyfriend I think about leaving him because I feel like he's out of my league?

I know most dating coaches/counselors advise against this because it's likely to make things worse and seems like an annoying display of validation seeking behavior. However, I've been plagued by these thoughts for a long time and I've been thinking about them obsessively to the point it's making me suicidal. I feel like leaving him without saying anything and never looking back. But just because that's how I feel doesn't mean I'm going to act on it. I don't want to make things worse but at the same time I want to be open and vulnerable. How would you react if your girlfriend said this to you?