pringle - sorry, that's shit.
I think it's quite common that when you meet someone through OLD, they still remember the sweetshop of all those other attractive faces, so keep going back to it.
Or they met their other half in real life and are just looking for a bit on the side. Branch-swingers, who need to have another relationship to jump to rather than risk being single for a while.
It's shit when you meet that type of person.
As far as meeting people you like who like someone else more, well that's dating, isn't it. Most new potential relationships fail, otherwise we'd all still be married and would have been since we were teenagers.
It's just difficult to go through it again once we thought we were settled down for life, in the case of most of us on here.
Remember rule 8 though. If it's not fun, stop. At least for a while.