Feeling betrayed. Need advice

So we've been together for 2 years. We are engaged and fixing to have a baby together. I'm being induced in two days. But today I lost my phone and used his to call mine, not really knowing how to use his phone cause I'm not aloud to touch it, I accidentally find snapchat. We're both not aloud to have this app for obvious reasons. His whole friends list is girls, and one girl he seems to like messaging is named long haired slut.

He's been hiding this from me and I feel betrayed... I have no idea what they are talking about or what pictures were sent. But if he was to talk to a girl, it's perfectly fine with me as long as he tells me about him talking to her. Same goes for me if I talk to a guy. He's also been texting a girl named Sabrina and he called her amazing, sweet, and other things like that. She stated to him that she's not aloud to talk to him cause she has a boyfriend but does anyways, cause she loves talking to him. Theyre being a little too nice to eachother.

What should I do? I hate to cause shit when he's working too jobs and we're broke as of right now just for this week (cause I haven't gotten paid) and a baby coming in a few days. But I'm honestly really upset and scared.