It's rarely that simple, although from the HD partner's perspective, it seems like that's the one and only problem. Fix that one area and everything else would be peachy, right? Wrong, particularly from the LD partner's perspective.
In order to help, we need some more information, really.
Do you know what was missing in your wife's life to cause her to first 'fall out of love with you' and then secondly, to seek another man?
Another way of asking this is: what was the OM providing for her that you were not (in her eyes)? Frequent affirmation? romantic gestures? things that made her feel special and cherished? a strong emotional connection and acceptance? a level of masculinity that swept her off her feet? What was there with him, that was no longer there with you?
I'm not trying to get you to rehash old, painful memories, but instead to look for clues as to what was missing -- that 'thing' that you had when you were dating and first got married, that got lost somewhere along the way.
Take care,
Bagheera
Me 50, W 45, M for 26 yrs S25, D23, S13, S10 20+ year SSM; recovery began Oct 2007
