I got online hoping to see something specific.
What were you hoping to see online?
I want somebody to be dead for sleeping with my girlfriend.
You should talk with the person, if you don't want them to see your girlfriend. It's illegal in many places, and immoral to wish death on someone. If you suspect that she isn't faithful, you need to talk to work it out, or break up with her.
Why can't I wish death on someone?
Because that kind of behavior is seen as psychotic. If you get joy from someone in distress you may need to see a professional to work through some issues.