feeling hopeless

About a month ago my so freaked out on me come to find out his ex messaged him. He told his best friend he loves me with everything but he "just can't shake her." He blocked her so I wasn't to worried because he works constantly for my parents and she lives in a different city. One morning we wake up and he gets a Snapchat from a name I've never seen, didnt think anything of it. Well he kept deleting the app and after his day off I open up Snapchat to find this name as one of his best friends. Come to find out, its her..

Our son is due in 10 weeks and I just cant understand why now after almost 4 years and 3 of them we've had our own house together. Any advice ladies? I don't want to break up my family but I dont want this to continue this way.. 😞 I can't play dumb for long..