You're living in a dream world because you are thinking in terms of "losing your wife." What you fail to realize is that you've already lost her!! Doh! If she's set up a myspace.com account and is looking to "connect" with other guys, than you've already lost her! Sorry to break the harsh truth to you pal, but I'd be an asshole for trying to sugar coat the truth.
Now, since you've come to this realization that your trust and marriage is probably over, what are you going to do about it? Are you going to confront her and whine and moan and cry for her to stop her extra-marital activites? End result: she'll walk all over you and abuse you even worse than now because she'll think she has you by the balls, and will use your emotions against you. Hint: you're a cry-baby p*ssy if you go this route.
Here is my advice: Say nothing for now. Gather evidence. Print out every email between her and "partner:" Set up some survillance, take pictures of some smooching, etc. Than, when you have enough evidence, go to a great divorce lawyer. Get everything legal in motion, unknown to her. Then, at an appropriate time, take off a day of work, and don't tell her. Take that day and put all of her belongings outside on the driveway. Call her at lunch, and ask her to meet you directly at a resteraunt for dinner. Act all casual and romantic. At dinner, announce the good news that she'll be sleeping elsewhere that night, and every other night from now. Tell her she can pick up her belongings off the driveway, and promptly move in with her new partner. Hand her the divorce papers at this time as well.
Go home, have a drink, and think about the new opportunities that await you in your now free-from-slut-wife life. Sleep like a baby knowing you're not lying next to an adulter any more.
Hope this helped!