Drama in Math Class

So there's this kid named Alex in my math class who thinks he's so smart. One day, I was working on our group project and I noticed he had a cheat sheet under his notebook. It was pretty obvious, everyone could see it. I should have said something right then, but I didn't want to get him into trouble or be the one pointing out his cheating. So instead, I just pretended not to notice and finished my part of the project. After class, though, this feeling of guilt stuck with me like a wet blanket. It's been bothering me for days now because deep down, I know I should have said something. But then again, he didn't say anything when I struggled through that last test. So it’s kind of like we're even, right? Or maybe not. Either way, it's eating at me.