In ACoK Stannis says that in Renly's bed, Margaery is likely to die a virgin. When Renly dies, Loras goes totally freak-out nuts and kills several other guys for just getting in his way. In ASoS he says to Sansa that the light of his life has gone and nothing can replace it. Jaime then says later on that if Loras keeps threatening Brienne, he'll take his sword away and "Shove it somewhere even Renly never found it."

Tywin also says at another point that Mace Tyrell had a problem with Loras as finding a good wedding match for a third son is "Always difficult, doubly so in Loras's case," so making him a Kingsguard is a good solution to the problem. Finally, in AFFC Cersei notes Loras's sexuality, pondering that just because someone prefers one thing, he might not be averse to sampling another (when musing whether to spread rumours that Loras and Margaery are lovers).