I'm annoyed by what I saw on my gf's timeline on facebook
Why are you annoyed by your gf's timeline?
She changed her status from single to engaged
You should talk about your relationship directly to your gf. You don't need to get so annoyed about it.
I'm also feeling upset about this. I think I'm going to ask her to break up and sort of prove my point.
You should talk to her first before you break up with her. Maybe this was a joke with her friends or to avoid having strange men message her online. You should talk about your relationship status with your girlfriend before making any big decisions.