It's summer, it's so hot that Eddie spends all his time at Steve's.
Everyone is convinced they're having a secret relationship, but Eddie defends himself by saying he's just there to enjoy Steve's pool. As everyone knows, he can't stand the heat, and Steve is kind enough to let him use his pool. If there's any secret relationship going on, it's between Eddie and the pool, certainly not between Eddie and Steve.
Everyone seems more or less convinced by Eddie's arguments and moves on to something else. Everyone except Robin…
And she's absolutely right not to be convinced, because Eddie and Steve have been having a secret relationship for several months already.
(Robin cornered Steve to make him confess the truth. He tried to deny it by echoing Eddie's arguments, but she gave him a “not to me, Steve Harrington” look, and he was forced to confess everything. As if he could hide anything from his platonic soulmate, anyway).
