First of all anyone that will give you that kind of ultimatum doesn't love you anyway. They may love control and they may think they love what they could make of you but it certainly isn't the kind of love that builds a good relationship.

If a line like that is drawn the best thing to do is start backing away, then turn and run. That's my opinion. No doubt influenced by the fact that I don't like ultimatums. Generally if I am told that I must do something then I wont. If someone wants me to do something they can ask and I will consider it unless it is something really way out like getting rid of my guns.