Would you be upset?

My fiancé has been liking naked girl's pictures on Instagram & started following some of them. I'm so upset & don't want anything to do with him anymore. What would you do? We talked about this kind of stuff & he always respected me and never went behind my back, but all of a sudden he doesn't care anymore. 
Update- I feel so betrayed right now and I'm crying. I've been feeling so depressed lately because of him and how he always looks at other girls even at work. He added all his female coworkers on snapchat, Facebook, Instagram and even texts them on his phone. I got over it but this one girl became too friendly and I talked it out with him and got over it, but this is crossing the line now for me. I really need to talk to someone, a girl who understands me, but I feel all alone and crying.