At the very start of the game, do you snoop at his laptop? You must not look at it, then you'll have to come out at the same day. When there are scenes like the one where you bump into him and he drops his towel, you have to stare at him so he knows you find him attractive.
Are you playing in the easy or in the normal mode? In the normal mode is MUCH harder to get Adam's route, I've tried it myself a couple of times and I didn't manage to get it, but using the easy mode and following the tips above I got his ending in my 2nd run. So try to play in the easy mode if you haven't already done it :P