I think that's his point. There is almost nothing to indicate it would happen if it were a hetero relationship, so to look for clues everywhere is stretching very very far.
If Korra was writing secret "I can only talk to you" letters to Mako, everyone here would throw themselves off a cliff because Makorra would be confirmed. There are only ten more episodes in the existence of LoK - it's the homestretch. I think we're safely in "what you see is what you get" territory.