Help?

This evening I was taking some pictures of my son and fiance on his phone to send to my parents who just moved nearly 800 miles away... While taking the pictures 2 notifications from snapchat came up from "Brittany💕" and another girl. What would you think? I have yet to say anything. This would be the 4th time he's done this to me and I just feel dumb. We will have been together 5 years this coming July, and we have a 3 year old, and we unfortunately lost twins this past year. I am a stay at home mom with no family here... I have nobody else close besides him and my son. I am so mad at myself for believing he would "change". I don't feel like I am good enough for him anymore since this keeps happening. What would you do if you were in my shoes?