Lulu went from Chappu to Tidus and then Wakka. It kinda felt like...

Chappu is dead, Kimhari is blue,
Auron and Tidus are gone, so Wakka will do..!

With that being said, I still do think they made a legit couple but Lulu being pregnant after 2 years considering it took her a while to get over Chappu in X seemed kinda like a stretch to me. They should've got married or something in X-2 rather than the pregnancy thing, felt too weird.