The knee-jerk reactions to this post are hilarious, "Dump her! Dump her!" If only all the SS members were such "saints" lol
First, OP said the girl is 23. 2-3. Hardly a mature women. Yeah, she wants to have some fun...what a f*ucking crime!! lol
Look, a whippet is a small hit of nitrous oxide or laughing gas as we know it in the US. Many dental offices use it here in the US. She's NOT a drug addict for having a little fun with it anymore than you're an alcoholic for having a couple beers or drinks. So yes, lighten the f*uck up people.
JFC, it's like she's shooting up heroin or smoking crack based on some of the "advice" here, LOL. No wonder so many SS dudes are perpetually single.
If you dump this girl for taking hits of N2O, after all the compliments you paid her in your OP about being a great girlfriend, you mind as well look for your next girlfriend in a convent.