So the plan had been to make himself scarce while the planning was going on. Roberto was big on parties but he didn't really do the planing of them. He liked to just show up and have the party happen around him, or maybe say things like; "We should go to this club, or get this champagne." So he had been going to just lay low and hope that Neena and Bobby took care of all the details.
That was the plan.
Until (as he was trying to quietly walk past where the part planing was going on) he heard them talking about sex. About no birthday sex? Wait? What was going on.
Walking into the room, he said; "No birthday sex? Why not? Is there something wrong?" That was directed at Bobby. And there as a touch of sympathy in Berto's voice, being laid up by some sort of ailment on your girlfriends birthday would be awful.