The title of this song (also shortened to that green gentleman) is about two opposites who fall in love. They are described as the day and night, or as the moon and the sun, to emphasize their differences. The song is also quite creative, telling a story about love through beautiful metaphors.
Lyrics mean that he is still worried about her and she has changed since they broke up; but, he is going to be able to move on. He doesn't want to waste his time chasing her, because she is probably just going to change her behavior again.
That he isn't sure how he can help her; but he is going to try to figure it out. He wants to be able to say to her that he loves her, and she can do what she wants with her life, without him having to worry about her.
Another verse mentions that he was young when he was dealing with her guilt; but, he is now older and he understands what he did wrong; he has a little bit of maturity; and he is going to be able to help her.
This song is an amazing example of how a band can write something simple and beautiful; it is one of the best examples of country-rock. It is a song that is so simple, yet so powerful, that it can be enjoyed by people of all ages. It is also a great song for any event, as it is so easy to dance to.