It is a little late, but I would like to give my take on this. It helps to know what the song “Good Riddance” is really about before deciding the meaning. The song was written by singer Billie Joe Armstrong of Green Day. It is a song about breaking up with his girlfriend (she was moving to Ecuador) and his disappointment that was attached to the break up. He was trying to be understanding and meant the song as a sort of farewell. The “turning point” is not a decision, but an event over which he feels helpless, a fork or splitting of their ways. I think he used the term “a fork stuck in the road” because it congers up to meanings. The first – a fork in the road… a divergence of ways. But also a fork stuck in. This refers to the slang “stick a fork in it, it is done” which means it’s over, finished, complete. By combining these two terms, the picture is that the relationship is over and they are parting ways.