You get that option by visiting him a lot at the office. And when I say a lot, I mean a lot - you need to get maybe six or seven unique scenes there, and have seen them all and have full heart to get it. That said, I got the bad ending the first time and just had to restore a couple of weeks, drop everything else, and visit him everyday at the office to get it - so it's definitely still fixable, even at the end!
Actually, if you know which scene you saw with him in the office last I could tell you how many you have to go... because I got a little obsessive that run and wound up counting them. XD