I think it's 100 percent natural to feel like a fool. But we are not fools, we were just fooled by someone we trusted and who betrayed us. I wasn't looking for evidence of unfaithfulness, were you? no, we trusted. That's not being foolish; that's being healthy and having someone abuse us for their own selfish needs.
Know that it's okay to feel like a fool. I know that feeling extremely well!!!! But I also know that I'm not a fool, unless I stay with him, and then I probably am. But your situation is likely different from mine; you likely have more good reasons to stay.
Hang in there. This journey sucks more than anything except death.