not to answer for roger, but in my eyes: You're right. Being immoral isn't black and white, in this case it's a line drawn in relation to your relationship to the friend you're considering stealing from. Now it's clear he obviously holds some value in the friendship since he's willing to fully disclose his ideas to you, ideas which he likely plans to do work on. By stealing his ideas you're not only robbing him of something he cares about and a potential income/customer base etc, but you're also betraying that friendship.

Your example of waiting 3 years is a valid one, the reason why the morality changes is because after 3 years he likely will care less about the idea (I mean he didn't do anything with it for 3 years, right?) because it's become apparent he doesn't care much about it, the robbing and betrayal have less of an impact, to the point where it's so much less of a deal that it's just overwritten by you friendship