What is wrong with me?!

I'm an idiot. I've stayed with a cheating man because we have two children together. It's legit been the same lady for 10 years. They haven't seen each other in 2+ years but still talk regularly (g chat, snapchat, text, sext, call) etc. I've honestly gotten use to her and know that he'd never leave me for her, she's too needy. And I play dumb like I don't know about it.. it's just easier for me. Well this last month he's added another whore. She knows he's married and doesn't give a shit. Why? Why are woman like that? Why are men like that? If you know someone is taken why can't you just walk away? Good Lord. I don't think I can go through this anymore but have no options as financially I'm not able to go anywhere and I don't have family to go to. Ugh.