Do you want to?
Here's a checklist.
Does she still bang you?
If the answer to all the above questions was yes, maybe chill out. Because if she isn't cheating on you and you make a big scene somewhere, you can uncheck that box in a hurry.
I guess you could follow her around like some creepy dude in a movie. Or you could hire a detective to watch her and take pictures of her like some creepy dude in a movie. Or you could sit in the corner in the dark and when she comes home you could turn on a dim lamp and surprise her with strange, soft-voiced questions like...well, you get the idea. Life ain't movies. Try asking her how she's doing once in a while. I guess, if you were really curious, you could slip in a telling question once she's comfortable, something subtle like, "How many fingers were inside you today?" (It's tricky because you will have counted how many fingers you yourself put inside her that day. Don't worry, you'll remember. It's usually between zero and six.)
Short Answer: You never know. If you bring it up with enough care and calm, you might end up getting a free pass to do some stuff on the side. And maybe, just maybe, you'll get to watch your wife get railed by a real man.