I'm going to throw my girlfriend under the bus to help someone else
How will you throw your girlfriend under the bus?
I know a vital information which will help someone else to get what they want from my girlfriend.
You really shouldn't help someone take advantage of your girlfriend like that. She probably trusts you to have her back and protect her, and throwing her under the bus like that betrays that trust. You should protect your girlfriend like you would want her to protect you.
That doesn't help me out at all.
You are being very selfish when it comes to your girlfriend and that is pretty morally wrong to do.