I figured it out and I feel like an idiot. You actually unlock it but the game doesn't tell you you do. It's the scene where Bo let's you fuck him. The only way I was able to have the game recognize that scene as unlocked was to not disclose to Bo who you saw having sex (Ben and Lou in the Pool room). He'll respect your integrity for that and the game will say he likes it. I don't know why it doesn't show up on any other alternative even though you unlock it. Due note that it only shows up while in game. When you're at the main menu, it will show up locked again.