Broken Bells "The After Disco"
Let me guess: It's about a boy with the girl, once had relationship. They both had an issue that made the girl asking the boy not to come to her past, but he did anyway. Once both of them on ship, the boy seemed attracted with the new 'disco' life, and get lost. When the girl found the boy chose another woman, she left him. And, when the boy realized the girl he really love left her, it was just too late.