TL,
I feel for you, hon. Sometimes, "F off" really means "F off" - so if that's what he said, that's what I would do. If you maintain that you support his next good move, in the spirit of being consistent, his latest moves haven't been good. So not contacting girlfriend, and not putting what you're not comfortable with on his canteen tab is consistent with your very wise boundaries. People can love us, but they can also play us like a fiddle.
He knows you are a scrupulously good person who tries to do the right thing. He wants your "right thing" to be giving him everything he wants. When you don't see things his way, he tells you to "F off!" So grant his wish!! Maybe girlfriend can put $ on his canteen. I know in my own situation, I permitted my so-called "good values", empathy and compassion to be manipulated. Then, I felt like I was victimized, till I realized I was allowing myself to be victimized by a clever user who also happened to be my son. It's not healthy. Just because I'm not capable of using people doesn't mean the closest people surrounding me weren't capable of that very thing. The serenity prayer helps in times like this. It's complicated - it's not just a black and white thing, there are gray areas in every relationship, and it's sometimes hard to navigate.
Be strong. it's wise to take a step back, not answer every phone call and get pulled into the vortex of their drama. We surely can't fix everything.
