Is it okay to have a Christian, who is living with his fiancée, to partake as a church decision-board member? The knowledge about his living condition was found out after he was selected to be a board member.
If you mean “living with his fiancée” as a euphemism for sexual immorality then there is some clear teaching in 1 Corinthians 5 about such. If “living with his fiancée” means “renting a room” then that is something else. I am not trying to be coy, but the meaning of words is important. The sexual standard in Scripture is the same for everyone, clergy, leader, or laity. There is not one standard for one group and another for another. These problems arise in church because we are all fallen creatures, living from time to time outside the Story of God. There really is not enough information provided for me to give a precise answer.