The following excerpt is from Chapter 10 of my book “Getting Control:  Overcoming your obsessions and compulsions”:

What if a friend or relative either refuses to get treatment or denies that he has OCD?  Since you know that OCD can be effectively treated, this is a very difficult situation, and it usually produces  feelings of hopelessness and anger in people close to the sufferer.

Sometimes you will have no choice left but to carry on with your life, while reminding the sufferer periodically that you are willing to help, that you recognize his shame and distress, and that people can get better from OCD if they get treatment.  Sometimes a person with OCD will not seek help until he hits rock bottom.  Of course, watching someone you care for suffer when he could be getting help is very painful.

In the meantime, you and other friends or relatives should learn more about OCD and seek support to reduce your feelings of helplessness.

…

In any case you should still try to follow the advice in this chapter about not helping the OCD sufferer carry out his rituals.  It is the sufferer’s right to not yet want help, but you should explain that you simply can’t knowingly assist him in making his problem worse”.