Well that storytelling technique is very common. A lot of stuff is insinuated in books, TV and movies, and leaves the audience to fill in the blanks. I see no problem with that in games.
And I agree with Kraidy. If they had time to come up with that threesome, they had time to discuss their feelings also.
And? We still don't know what transpired. At all. In fiction, when something happens off screen, someone else provides the information necessary for the viewer/reader to follow the plot. It doesn't happen here. This is a dead end.
The scene might as well be a developer joke for all we know, given how out of character it is for all involved.