I got cheated on

I'm 18. He's my first boyfriend. We were dating for two months and the day after my graduation party he said it "wasn't going to work anymore". He gave me excuses and what not, and honestly I saw it coming either if I broke up with him or he broke up with me. But I found out today he cheated on me. I saw him in a parking lot with the girl, and later that day I saw things on Socail media making fun of me for being so oblivious because I gave him the benefit of the doubt when he said the bruise on his neck was from being "pinched in a wrestling match".  I'm not sure how to handle this. I don't want it to blow up into this huge petty drama, but I'm still upset over it. Am I wrong to be?