I can relate to your story. I was scheduled to be the donor for a friend. I had myself all psyched up to donate and was preparing to go. Then, my friend had another donor that felt compelled to donate and that they wanted to use and I became the backup. I put the entire process out of my mind and moved on with life. Two weeks before the schedule surgery, the other donor backed out. I had to quickly change gears and mentally prepare for the surgery. I also felt like it was an emotional roller coaster, but I believe everything happens for a reason.
Since you are a priest, I'll share a "religous" moment I had the day after the surgery. Throughout the process, people kept telling me how I was making huge sacrifice. The day after surgery, I had some complications and it was a really rough day for me. As I was laying there, I kept thinking that it was unfair that I made the big sacrifice, but I was the one in such rough shape. Then I thought about Christ sacrifice on the cross and it really put things into perspective for me. Here I was, with nurses and doctors taking care of me, pain meds and a large group of friends and family supporting me, yet Christ had none of that on the cross and he was still willing to go through a lot worse than I went through for me. That really made an impact on me. I realized I had nothing to complain about.
Good luck with this and I'll keep you in my prayers. It is a wonderful thing you are doing. Even if it doesn't work out with this person, maybe there is someone else who could use your kidney.