There are many ethical and legal principles at play here, and it is up to the group to decide what to do or not do. Some possible considerations include the client right to autonomy and self-determination, the client right to confidentiality, the client right to receive treatment, and the client right to safety.
The client has the right to autonomy and self-determination, which means that he has the right to make his own decisions about his treatment and care. However, he also has the right to receive treatment, and if he is not taking his medication as prescribed, he may be putting himself at risk of serious health complications. In addition, the client is sexually active with several women, and if he is not taking precautions, he may be putting them at risk of contracting HIV. The client has asked that you not contact him at his home, but you suspect that his girlfriend knows where he is. You may want to consider contacting her to see if she can help you get in touch with the client and convince him to seek treatment.