I'm letting you, tell the police I said it's cool so long as you don't drill all the way into the guy your girlfriend is already datings apartment next door..

No it will be grand if you use good size 5 screws. Only screw as far as the plasterboard don't screw the screw in all the way to the concrete. If you have 20mm of air you might use a 5 x 70 screw. A red rawl plug will hold it good and tight.

Adjust sizes for America i suppose. I don't know your system. I'm in mm

Use a 5.5 drill bit.

Drill the hole. Put the rawl plug on the end of a long screw push it into the wall and then twist it out.

You sound like she needs a new man in her life.

Anyway, you should have used rawl plugs in the concrete with screws long enough to go into the concrete.

You can still do this, the cabinet will hide the hole in the wall. If so much plaster in gone that you can't hang it used some wood to bridge the gap and screw that to the wall, filling the hole.

Why does the girlfriend have to pay for it,

The only thing that stops a bad guy with an explosive egg is a good guy with an explosive egg.

Its Britney Bitch.