As long as she finds you interesting and somewhat of a challenge, she'll stick around. (Given she's interested from the start)
Be all open and saying 'i (L) u' all the time, a large percentage will -even not intentional- lose interest because they already 'have' you completely, no more 'challenge'.
Woman want the tough guy, not the soft one. And even tho they think they want the sensitive one, they don't.
(I've only ever met one girl who was 100% dedicated no matter what, maybe she was 'the one', but at the time i wasn't thinking right and let her go.)