I think a lot of people here are missing the point by trying to figure out who the promised girl is... I think the whole idea in the end was that it didn't matter who he promised in the past, he's in love with Naru now and that's who he belongs with. He made promises with several girls, but he can't let that keep him from going on with his life and loving Naru.
I own nothing Love Hina related, unfortunately
. I want a Motoko of some sort (she's my favorite anime character and my first anime love ;D ) but I hate how scantily dressed all of the LH figures are =P . Some of the resin kits are ok, but expensive and I'd never painted or assembled models before =P