I [41F] just found out my husband [40M] cheated on me. I have no idea how to confront him.

I just got a facebook message from a woman who had been casual sexual partners with my husband on and off for over a year before realizing he was married. She sent me dozens of screenshots of their conversations, which included flirting, sending nudes, and planning to meet up for sex. The times they planned to meet match up with times my husband said he was working late or spending time with friends. She believes he was probably cheating on me with others but has no solid proof of that. Somehow I never even suspected. I don't even know where to go from here. I want to confront him but I don't even have the words to tell him how betrayed and devastated I feel after twelve years of marriage, four children, and a move across the country with a man I don't even know anymore. I have no one I could ask about this, so I'm crowdsourcing some advice.