Hi Miriam!
Do you mean pray for this man as your future mate, as in asking God to give him to you?? I have a super nice guy that I know but I don’t ask God to give him to me…he might marry someone I don’t even know! I ask God to help him to grow in Christ and love Him more. God’s ways aren’t our ways. You say he’s in a relationship? Maybe God wants someone else for you? Ask God about this man, ask Him if He wants you to pursue him or not. Pray that his love for Christ will increase and that God will use him powerfully. I’ve been thinking a lot recently about how God reveals whom we may or may not marry, and I talked to my mom about it and she said that if God puts obstacles in the way of something, He might be saying no. I’m not saying that’s what God is saying to you; you need to examine the situation and ask the Lord. Hope that helps! I’m praying for you!