I still think Lulu was more hung up on Chappu than she was in love with Wakka by the time FFX-2 rolled around. Sure the game was 2 years later, but I don't know if the whole dating your dead fiance's brother is a common thing in fantasy-land.

I do see how close though that death brought Lulu and Wakka. They didn't just avoid each other and move on, they let it bring them together and be a comfort for each other as they began their pilgrimage with Yuna and the crew. They worked together to get their minds off Chappu's death by partaking in the journey.