personal opinion?
walk away... a matter of respect... if you do not want this to
happen to you, you should not do this to others also...
if in the future, without you around, they go their separate ways,
then maybe you can make your move...
the benefits are:
- you have a clear conscience
- they can make their decision without someone there causing doubts
and influencing a decision that should be made by themselves
- you show them the respect and they will offer you the same
respect
there would be more if you just think about it...
i wish you peace and happiness 
