FF IX Ending (SPOILERS, don't say I didn't warn you)

Well I just finished FFIX a couple of days ago and I have to say it’s now my favorite (It was VI). I just got one question about the ending:

During the last few scenes Beatrix plans on leaving the castle but Steiner stops her by telling her he lover her. My question is: Why did she want to leave in the first place?

This just a guess but maybe with the big battle over, and her being able to do little more than protect them from a few dragons, she felt like they no longer needed her to protect the queen, who fought well on her own.
So maybe, just maybe she felt like she had no more use at the castle, and decided to leave!

Guilt over helping Queen Brahne and not stopping her when she had the chance, combined with the fact that there are no more threats to Alexandria might hav something to do with it.

I just thought is was because Dagger had Zidane now to protect her. It just seemed weird to be because the whole game Steiner and Beatrix were all like “Protect the princess with you life!” and then she just wants to leave.