I think that he stole her away from another guy because she feel for both of them. So she went on with it, she left the other guy for him, but after a while they started to see that she was much happier with the old guy. His saying that the both of them are ok with each other, but she won't be happy with him, she can only be happy with the guy she was with before. But before she goes, he is asking that he can have one last dance before he knows that he has to let her go for her to be happy. He's saying that though he can give her everything there is one thing he can't give and only the other guy can, because that is what feels right.
I think that he stole her away from another guy because she feel for both of them. So she went on with it, she left the other guy for him, but after a while they started to see that she was much happier with the old guy. His saying that the both of them are ok with each other, but she won't be happy with him, she can only be happy with the guy she was with before. But before she goes, he is asking that he can have one last dance before he knows that he has to let her go for her to be happy. He's saying that though he can give her everything there is one thing he can't give and only the other guy can, because that is what feels right.