Somehow those who are in love never think
I'm surprised that there are people who doesn't mind being the third party. Especially those where one is still in the his/her illusionary heaven. Even if your lover would eventually give the the current relationship to move into a new one with you, what makes you think that you wouldn't be the next in line, in your own illusionary heaven?
And if you know that you're the third party, why break up a possible relationship?
Just leave in peace.
and everyone can leave in peace.