I believe that by the time the offending spouse decides to have an affair, they are checked out beyond the point of wanting to offer you an apology. In fact, as strange as it seems, they usually feel they are the ones who are owed the apology.
They are generally carrying so much resentment at the point they engage in the affair, then they feel guilt, and the only way to deal with the guilt is to convince themselves that it's your fault. Then they feel badly about that, and get mad at you for making them feel badly. It builds on itself and that's often why they are such monsters to the LBS.
They start with pain and anger, what they do to escape the pain and anger brings them even more pain where you are concerned which then makes them angrier.
It's not at all unusual to never get a sincere apology after an affair, as a matter of fact, I would say it's the rule. The best you'll usually get is "I'm sorry for how it made you feel" which is different than "I'm sorry I did it."
For some, the lack of an apology crosses their line and they cannot reconcile. For others, they get along without it.
WRT your wife, chances are she's not feeling fulfilled, and that her needs are met in your marriage. THAT problem was not addressed after the first affair, which is what lead her to stray again.
The fact that her needs were not met might be 100% your fault, you may have mutually contributed to it, or it may have nothing to do with you and everything to do with her. Generally it's not black and white.
A good thing that DB can provide you is the tools and education to understand what you need to do to meet an emotionally healthy person's needs. That knowledge can be empowering.
Some people get in the way of having their own needs met -- they're afraid of intimacy, they have expectations that are so high no one could meet them, they are narcissistic, they are addicts, etc. If they are not willing to do the work on themselves to address these issues, then your chances of a healthy relationship with them is fairly low. In order to work on the issues, they have to be motivated to do so. Sometimes you can provide that motivation and sometimes you can't.
Unfortunately, if you feel you're owed an apology, you're right, but you'll probably end up waiting a LONG time to get it if it ever comes at all.
Accuray
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015