Just want to offer hugs and moral support.
I've been in your exact position, so I know what it's like to have the feelings you are experiencing... and feeling somewhat "helpless" while the established couple figure out what it is they want. In my situation, they made it clear that no matter what, THEY came before WE. My opinions would never matter as much as theirs... Therefore, it was easy for me to walk away from the relationship.
Sex between a man and a woman can be absolutely wonderful - provided you get between the right man and the right woman. ~Woody Allen