I just want to close my eyes and wake up and be happy again.
I know that feeling. It doesn't work that way, though.

It is pretty common to get accused of untrustworthy behavior by an untrustworthy spouse. I got it. lots of people get that.

My parents and brother are coming this weekend and she is sleeping in our bed for 3 days.
Maybe you should directly address this with her, before they arrive. like now. re-open it and say - is this weekend arrangement going to work? Why are we hiding it anyway? If we can't tell them we're having trouble, who can we tell? This happened when my wife's father came to stay with us. Instead of coming to the room, she just pretended to not be sleeping where she was. Hid her bedding. she was always the last one to bed and the first one up. it was so dumb. These are the people that could have helped us. She was hiding from them.

There is no shame in having trouble in your marriage and working through it. Everyone has trouble.

One minute I am pissed off and detatching, the next i am crying my eyes out. I really don't know if I have the strength to see this through or if I even want to.
I know the feeling. But the truth is, if you are pissed off you are decidedly not detached. Detachment is not "pissed off and not speaking to the other party."

Detachment means, in control of your emotions.
I know it's hard. What can ou learn from the situation?

When I played sports in school, if the team got beat, if we screwed up in the game, in the next week's practice, we'd work on the plays where we screwed up. We'd run them in practice except we'd do it the RIGHT way this time. Can you do this in your mind with the exchange over myspace etc. How would you have acted if you were the man you wanted to be? Play it over in your head. when she accused you of looking for girls, you would be a big enough man to say, "now why would I do that when I have what I want right here in this house?" you would be strong enough to empathize: "oh, you don't trust me. I see that. I wish you would. how can we get to a point where you trust me again?" or you would be strong enough to not engage. "No. I don't do myspace. (end of discussion)"

If you do it right in your head you may be in a better position for the next time. And yes, there will be a next time.