I feel stupid

All this time I’ve been tagging him on stuff about how amazing of a husband he is.....till tonight. He is drunk and asleep and i went to get his phone to put it to charge as he has work tomorrow. And i saw the message that made my heart beat faster. And when i looked at the chat history.....i felt my heart break. He’s cheating on me with a coworker. The saying of once a cheater always a cheater is true. We’ve been married since June of this year. We have a 1 year old daughter and a 3 week old son. And i want a divorce. I’m tired of everything. I don’t want to be with him anymore. He had his messages hidden. He doesn’t help with the kids at all. Hasn’t changed a single diaper. He always wants me to do as he says. But never listens to me. I’ve seen sexual videos he has recorded of us (me giving him a handjob since I’m 3 weeks postpartum) and i knew nothing about the videos! And videos where I’m to my side and he’s pulled my panties down and smacking my ass. I honestly believe he only got married to me so i can get him legalized. (Ever since we got married he’s been pressuring me into going to a lawyer to start the process). What do i do? Am i overreacting? I don’t want to lose my babies! Please help...