He Cheated and i'm almost 6 months pregnant

Here he was sleeping peacefully on the sofa and i was rubbing his head thinking how could I love someone so much more than him and our son on the way. He just got an apple watch for his birthday and I hadn't really checked it out yet so I decided to. I click on his messages and there it goes "Goodnight beautiful see you in the morning" to another girl who wasn't me. Him and I, I thought were on a good path together. I saw the rest of the messages between them and I read just regular conversation to how he could "make her finish in 3 minutes". What do I do?😞 these hormones make everything and this hurt 10x worse. We were saving for our son and Just got a 10 week old puppy to raise with our son and my emotions are over the moon right now. I just need some support and uplifting. Maybe another woman has gone through this and can give me some advice 😓