The enigma is in the ending. Daniel has lied to Rober about looking at plans for a loft development "upstairs" with Santiago. In fact, as Rober is told by an inebriated woman, what is going on up there is an orgy. He joins in but we don't know with whom.
Prior to this we see that the relationship between the guys is drifting into irrelevance. Rober is tempted by a handsome stranger on the commute from work but backs out - that's the outline of the plot given by IMDb. There's more to the film than that though. Home life is in a rut and stultifying. Some affection breaks through as when the couple cuddle before going out. The lads are clearly going to remain an item.
Temptation beckons however. We can't be sure who it was with though.
