Couldn’t Renly have thrown his lot behind the Tyrells BECAUSE he loves Loras? Like. Robert left a lot and then he’s king. Stannis and Cressen left. Now he’s surrounded by people who only see a lord, not Renly. And then there’s Loras. So he plots to make Margaery a queen in order to prove his value, to make Loras stay. I also think Loras loved Renly for Renly. Renly was just insecure, so he listened for Tyrell desires and tried to fulfill them to silence those insecurities.