I find myself wanting to give you some hope that things may work out when your GC is an adult. Although Magic makes some good points on you don't know if you GC will become an adult you like, I am a perfect example of an adult child being able to forgive and have a relationship as an adult.
My parents divorced when my mother was pregnant with me. My father was an alcoholic and a womanizer during my parents 9 year marriage. I have a brother that was 8 when the divorce occurred. My Mother told me what had happened when I was around 14, as far as the truth about my father. He was selfish and didn't want to take the blame for the divorce, so told everyone that my Mother had cheated and I was someone else's child. Very bad marriage for my Mother. Because of the lie he told, he had to pretend I didn't exist my entire life. My Mother was going to give him visitation (although he didn't deserve it because he was not helping financially) but he had to stick to his story and say he didn't want to see a child that wasn't his. He saw my brother sparadically for a few years but had not changed and eventually my Mother put a stop to it. So I never met him and my brother did not see him after the age of 12.
Fast forward. I was 25 and an accidental meeting with his new wife occurred. I had known his new wife for about 6 years, but just didn't know she was married to my Father. My children and her grandchildren attended the same skating party and my Father was there. When he saw me, he knew immediately that I was his daughter because I looked exactly like my Mother. He left in tears without confronting me and later, his wife came to me and asked me if I knew who my real father was. I told her yes and she said, "Do you know his name?" When I told her, she about fainted and looked at me and said, "Oh my, I am married to your Father." It was a long road for me to meet him. It took me over 6 months to decide to have that meeting. He had changed from the person that was married to my Mother. He had been sober for 10 years, was attending Church and was a different person. I spoke to my Mother at length, and she was very open to me meeting him.
I am very glad that I did. His first words were, "I was terrible to your Mother, you and your brother. I make no excuses. I was a bad person. I hope you give me the opportunity to be in your life now that I am in a better place." Did I love him? No. Did I like him? No. I had to work through MY anger and I chose to forgive him. This will sound selfish, but I forgave him because I needed to do it for myself. It wasn't for him. I had carried an anger around for a Ghost and in forgiving him, I was able to let go of that Ghost. I have now had him in my life for 17 years, and he has been a great Grandfather to my Sons as well. It wasn't always easy, because out of respect for my Mother, I had double birthday parties and such for years to keep them apart. But it was worth it.
Now, I told you this to say this. About our 3rd get together, he pulled out a scrapbook. I had played tons of sports in school and received academic achievements as well. He had watched the newspapers and had cut out every article I was in throughout my life and put them in that scrapbook. He had kept up with me through the articles and had lovingly preserved every one of them. At first it kind of took me back and I wanted to say, "If you took the time to do this, why couldn't you take the time to see me?" But then I realized, he gave me a wonderful gift by staying away after he had sobered up. As a teenager, I would not have appreciated him coming into my life all of a sudden and needed to be old enough to be able to see the situation as an adult. When I realized that, the scrapbook made me break down and cry because I realized he had cared enough about me to keep up with me from a distance.
I think the journal idea is great. That, or a scrapbook of sorts like my Father did. He told me that even if I had never wanted to see him, it gave him peace and therapy to do it for himself. If your GC turns out to be a good person and a forgiving one, it could go a long way. But you also need to be ready to accept that things may not turn out that way. And you can't dwell on it. You have to live your life with the attitude of maybe someday but not today.