The third arm in the play represents "the discovery and development of genius or talent in an otherwise unremarkable individual."
So, if he sees the the one cares deeply for walking with her new love interest (an otherwise unremarkable person whom she has found remarkable qualities)...he'll understand. It's only recently that he's come to accept the situation...thus "but, you shoulda been in my shoes yesterday".
Check this out... http://en.wikipedia.org/wiki/The_Man_Who_Had_Three_Arms
The third arm in the play represents "the discovery and development of genius or talent in an otherwise unremarkable individual."
So, if he sees the the one cares deeply for walking with her new love interest (an otherwise unremarkable person whom she has found remarkable qualities)...he'll understand. It's only recently that he's come to accept the situation...thus "but, you shoulda been in my shoes yesterday".