Maby...
I love your submissions and can never really understand them on mp own and so always read the review section afterwards to understand them :P However, there are all kinds of different "theories" so I'll just give it a shot.
The man calls some woman, presumably his girlfriend, and her not answering signifies she's gone. Why? Probably because he's a workaholic, and/or put all his earlier priorities in his proffesional achievemnet. As a result he never met anyone or drove away the loved ones he had. He's says he's sleeping at the office out loud as if he's finally admiting his situation. He's not only sleeping AT the office, but WITH the office, as opposed to sleeping with someone he loves. He sleeps at the office, because that's all he has left.