ok a secret can be anything you think they would be hiding. for answer i can see that maybe he didn't like someone in the group, maybe he purposely allowed la di da to kiss him even after knowing fifty fifty liked her, he thought not shy was never a real friend to begin with, anything really.

red - Strong-willed, straightforward, well-grounded, hard worker, competitive, realistic, impulsive
blue -  caring, intuitive, steadfast, freethinker
violet - wisest,  independent, observant, intellectual, extroverted and authoritative