Can my husband subpoena our son to testify concerning a phone conversation that my son and I had?

This is my divorce case. My son was very intoxicated during our phone conversation and misconstrued some of the comments that I made. During the conversation, he told me some personal information concerning his affair with another woman outside of his marriage. He is now in a very bad position as a testimony to our conversation is based around his affair. Under these circumstances, can he plead the Fifth? His wife has never found out about his affair. He would like to keep it this way.