Buffy was delusional and read way too much into the situation.Parker's behaviour after he and Buffy slept together definitely puts him as a potential contender, but I honestly don't know whether Buffy read too much into the situation whereas Parker saw it as a bit of fun, or if he genuinely led her on just to sleep with her. They'd been out on a few dates so he put in the time which seems a little bit too much effort if all he was after was a one night stand.
Spike, even Joss called him the long haul guyNo, I don't think that. I think many of her boyfriends were a matter of convenience and she could not be without one so she sometimes jumped on the closest (and easiest thing) she could find. I think there was only one that could be considered the whole package.