Was it a requirement to be married to be a member of the Sanhedrin court? Was the Apostle Paul a member of the Sanhedrin, and if so, what happened to his wife?
There was no requirement to be married to be a member of the Sanhedrin. By the days of Jesus, it was mostly a political appointment. The requirements, which were quite vague are discussed in: "What were the requirements for being a member of the Sanhedrin?"
It was suspected that Paul was being groomed for the Sanhedrin, but there is no evidence that he was actually appointed to the court. Actually we can safely assume he wasn't a member because when he went to Damascus, he did so as a representative of the court, not as a member of the court. "Then Saul, still breathing threats and murder against the disciples of the Lord, went to the high priest and asked letters from him to the synagogues of Damascus, so that if he found any who were of the Way, whether men or women, he might bring them bound to Jerusalem" (Acts 9:1-2).
Paul was never married. See: "Was Paul married or a member of the Sanhedrin?" for more details.