What would you do? (EDITED)

What would you do if you saw your significant other Snapchat another girl? I know the girl. She posted a selfie on her story & he replied “😍😍😍💞”.

We have a baby together.

I woke him up last night to ask him what it was about. His response was “you woke me up for THAT?”

What I meant, is would you leave? I just feel at fault for not always putting the time in to look good for him. We’re his intentions to cheat? What does he gain by letting her know he likes what he sees? When he has a wife and baby at home.