I think all of this is done to see if that "in love feeling" can be recaptured. Once they realize it's not something they actually feel for us, that's when they are convinced it's time to leave. They don't realize that genuine love goes deeper than that "in love" feeling.
Sometimes they don't even try to "recapture the in love feeling" especially when there is already another woman in the picture. They take this new "superficial love" as the real thing because it stirs their "passion". Those are pretty strong hormonal feelings - something that long term marriages just can't compete with, hence the spouse looses. When the affair is over some of them may realize what they have lost and come back and some just go on a quest for a new hormonal "high".
M53 H54 D17 M33Y T38Y Bomb OW 09/09 OUT 10/09 BACK 11/09 OUT 01/10 WANTS TO R 04/10 BACK with OW 05/10 Wants to Reconcile 05/11 I said NO
