[M.B.E.]

"Also why not reraise the river? I don't think it's likely he's putting you on a diamond draw after your aggression early in the hand."

Kevin really can't threebet the river because of the chance his opponent has KK or QQ for a full house. Also he might have an ace-high flush.

I don't understand why the opponent told Kevin "I can't believe you bet the turn". Maybe the opponent mistakenly believed that he had three-bet the flop. Checkraising the flop and betting out the turn against a preflop raiser is a standard play.