Why the ending? [SPOILER]

Why exactly would anyone think it was a good idea for Julia to get back together with Carlos, who is obviously a first class moron, and the most gullible, naive, obtuse individual in all of Spain (with Ángel a close second)?

And why, if Julio actually cared about Julia, would he drop the "I love you" bomb in his goodbye video? Way to re-complicate the situation, pal!

I get that it was supposed to be a quirky comedy and all, but even in quirky comedies, character motivations and decisions need to feel plausible, and I didn't buy anything any of these characters did.