Pick the weed. I don't think you have to find a girlfriend that will smoke with you - getting stoned together isn't an integral part of a relationship, but I would say that there's no point in staying with someone who'll give you ultimatums like that. If she was making you choose between her or your friends, you'd probably pick your friends and not even have to think twice about it. Someone who puts you in the difficult position of having to pick them or something else you value just isn't worth it.