Bruce isn't here for any of the usual reasons. He doesn't want to socialize, he doesn't drink alcohol except an occasional single beer, and he's not much for live entertainment. In fact, he's made one circuit throughout each floor, poked his nose everyone it could be poked, and then come up to the rooftop to stand and look out over the city.

He's here because Betty got hired as security and he's enough of a stalker to find that out. He won't be invasive, or do the bad boyfriend thing of telling everyone else that works here that they better treat her right-- he's not her boyfriend, he doesn't have claim to do that, and even if he did, he wouldn't-- but he feels a compulsive urge to keep tabs on her. Betty doesn't need it, but his peace of mind does.

Mission accomplished, he's idly loitering and debating leaving, nursing one half-full beer.