I think he cheated on the girl he's singing to. "...for loving me LIKE YOU DID BEFORE." Before?
Most of the song is about his love for her and how amazing she is. But I really think she is giving him a second chance. Surely he felt bad about cheating and really is sorry; so he wrote this song for her to show how much he actually does care. He had to include the "before" part just to clarify that he screwed up and that she is better than him. I think he's saying "thank you" not only because of how wonderful she is and because of the positive impact she's had on his life, but also for giving him a second chance.
I think he cheated on the girl he's singing to. "...for loving me LIKE YOU DID BEFORE." Before? Most of the song is about his love for her and how amazing she is. But I really think she is giving him a second chance. Surely he felt bad about cheating and really is sorry; so he wrote this song for her to show how much he actually does care. He had to include the "before" part just to clarify that he screwed up and that she is better than him. I think he's saying "thank you" not only because of how wonderful she is and because of the positive impact she's had on his life, but also for giving him a second chance.