Some people here seem to think that if an ultimatum is directed at a CD then the answer is to treat the crossdressing. Is it not obvious that the answer is to treat the reasons why a partner would feel the need to resort to an ultimatum?
We need to keep our heads straight. There is nothing wrong in crossdressing, the wrong is in the issuance of an ultimatum. The issue to be addressed is the partner's feelings through some form of counciling.