I don't want my girlfriend steeping out without me.
What happened to make you feel this way?
I felt like such a loser when I told her about my problem with feeling abandoned and she didn't even care.
I can understand how you are hurt, but you shouldn't tell your girlfriend how to behave. Trying to control her will only make her get angry at you. You can't expect her to always drop her plans for you.
You're right. A girlfriend doesn't deserve to be treated like that.
No one does. Let her be and when she comes back you can tell her how you feel.