fwiw, and i quote,
All people are free to move on from their relationships, should
they no longer be satisfied with them, for any reason; this shall
most likely happen if the other party fails to see to their needs,
whatever they may be.
that said, talk about stealing somone/win him or her over/etc is
trival, perhaps even to the extent of being irrelevant/missing the
point.
if one is willing to leave an existing relationship for another,
then it implies at least that he/she is not entirely satisfied in
the existing relationship.
some of the issues that pops up: why didnt he/she leave sooner? why
did he/she choose to stay on? why leave when someone popped into
the picture? if someone better didnt come along, will he/she stay
in it? are there more important things to his/her well-being?
...
either way reveals quite a bit about the person in question.
but more importantly is how one see those traits. and be prepared
for answers, if any, that arent expected. 
