When my girlfriend was gone I fooled around with her computer for about an hour.
Why did you fool around with a computer that is not yours?
I wanted to see if she was active on dating sites. I also wanted to know if she was cheating on me.
It is wrong to look at other people's computers and spy on them. If you do not trust your current girlfriend then you should not be in a relationship and it is time to break up.
I'm going to deny everything if she finds out. I don't think there is any way that she would though.
You need to be more respectful of her things and to use her computer only when she lets you. Spying on her and looking at her internet history is wrong and crossing the line.