How would you react?

Bailey
You and your SO have been together for over a year and one day he starts acting weird but you don't know why. He begins to avoid you when certain girls are around, you still think nothing of it. He has a sports event and you go to see him play. You get there and he's acting normal. Four other girls show up to watch him. The one he knows best is cheering for him and gets scarred when something bad happens. He goes and sees the group of girls before you after the game and snapchats the other girl for the rest of the night. While ignoring you. What do you do?