Well. I guess he’s cheating

I’m so hurt. I have an 11 month son with him and we’ve been together for 2 and a half years, and this morning I went to text his boss that he was sick and saw this

However she is his best friend on Snapchat and they spoke last week apparently but there’s no messages from when we started dating to show proof. I don’t know what to do, I added her just to see if maybe she could confirm it so I know for sure but it’s been killing me all day talking to him. I need to know but he’s also been abusive and mean before, I’ve already been planning an out, this is just the part needed so I can get the ball rolling now. Is there any advice for going through this with an infant? Or just in general?