When a marriage is broken, as a consequence of one partner choosing to be intimate with someone outside of their marriage, it often puts the 
"faithful" ones divorce recovery in jeopardy.
He or she often ends up in self imposed suffering for many years,
sometime for the rest of their lives...

Me - WE - You 
The Me and the You are the only ones who form the 
"WE MARRIAGE RELATIONSHIP."
Both the We and the You are solely responsible for maintaining 
their marriage system and to keep the union active, functioning 
and comfortable for each other. 
As soon as one chooses to no longer maintain the WE marriage relationship,
the system becomes lopsided.
As consequense their lack of nurturing of their marriage and lack of maintenance eventually breaks the marriage.
It takes only one of the partners to break the WE marriage relationship. 
So even if the other partner wants to retain the WE  relationship, that partner is powerless over the other partner's  choices to break their marriage relationship. 
Rarely do both parties come to a mutual agreement to break 
their WE  marriage relationship. 
No one, but no one, outside of the marriage breaks up 
the WE marriage relationship. 
The marriage can only be broken by the ME or the YOU. (One of the partners in the marriage.)
They are the ones who made a contract, commitment, and promises to each other.
~*~
When the marriage is broken, both spouses must now come to accept the fact that their marriage no longer exists. Once they do that, then will be able to go through the process of divorce to extricate themselves from each other from their  financial business, and  everything physically and emotionally. 
Once that is done,(the divorce), each will now be able to continue
living the rest of their lives, either in singleness or in another marriage. They will be emotionally free and present for another.

Failing to accept that their marriage is broken and no longer exists, 
that partner remains in limbo.
(This most often happens to the Initiated one, but not always.) 
Their former spouse (the Initiator) may have divorced them legally and emotionally, and the initiated one may have had their lawyer handle the legalities, but the emotional divorce was never done. It gets put on hold. 
So, now with no acceptance that the marriage is permanently dead, i
t means there is nothing to be grieved. 
The pain of reality is avoided. 
So, year after year, sometimes for the rest of their lives, the initiated one remains firmly emotionally attached to their former mate with pinening for their lost spouse or with vicious anger. . . But.... in most cases where a third party entered the picture prior the announcement of the broken marriage, this vicious anger and blame 
gets completely misdirected 
and becomes aimed directly upon the third party, rather than on their former spouse.

So now the pitiful Initiated person remains stuck in perpetual blaming, anger,
living his or her life from the standpoint of a victim. 
The lack of processing their loss or doing their emotional divorce 
from their former spouse,
now runs his or her life.

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Yes, of course it was absolutely incorrect for one party, while still in marriage, to break the commitment, the sanctity of their marriage and
their marriage system, 
by feeding their intimacy appetites with someone other than 
their marriage partner. 
Nobody made them do it. It was entirely their own choice. They are completely responsible for their own behavior. 
Your former partner was not your underling or nor your tin god, but an equal to you. 
Each of you behaved how you chose to behave in your marriage. 
You both made choices that either enhanced or diminished your marriage relationship. 
Had your partner been kind, honest, conscientious, principled, honorable, noble, straight, etc. she or he would have enlisted you in solving the problems that were drawing you apart, etc.. or at least  he or she would have had the backbone to end your WE marriage relationship before 
becoming involved physically or emotionally intimate with someone else.

For a while, after a marriage has broken, it is natural and helpful to feel anger while the detachment (emotional divorce) takes place and for awhile it is okay to irrationally blame a third party for the loss of your marriage.
But beware!
If after two years after your loss you find yourself still blaming the Third Party, waving it as a flag of "See.. I did not fail in my marriage relationship.It was someone else who made our marriage fail," or a flag to hide behind rather than to take charge of your life, or making it a flag of an attention getter for "poor pitiful me," or a blindfold to prevent taking responsibility for your behaviors and your role in the marriage or a shield to no longer trust members of the opposite sex, etcetera. . .  then  this anger, 
blaming and finger pointing has now become detrimental to your very life. 

Most everyone who has experienced a third party involvement, prior to divorce, do fume. They fume from every orifice, at the very sight of these two words - Third Party!  Their eyes remain squarely fixed in the direction of their pointer finger. A pointer finger  that  is pointed directly at the third party and has now turned into stone. 
These pitiful ones, fixated on the third party, live by the code.. .It is "my right and privilege to vent my anger at the third party" and they freely exercise their right consistently, year after year after year,
repeatedly injecting their poor body with the potent chemicals of cortisol’s and adrenaline's  that are released within them every time they think angry 
or automatically think of Third Party.

Five, ten, twenty years later or more... this fixated person will
have become calloused from chronic anger 
and will have become deaf to their screaming feelings that have been begging them to change something that is causing them unhappiness... and they may never hear their feelings cry out for change until  their immune systems and major organs finally can no longer withstand the attack of the potent chemicals from the constant rage. 

That will be their wake up call and maybe, just maybe it will motivate them to reach for the medicine that will heal them from their old angers and they will find the strenght to get their eyes and pointer fingers off of the Third Party and finally, finally complete their emotional divorce. They will do the work to do the  emotional divorce from their former spouse which will set themselves free from their self-imposed shackles.
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If you are reading this and you were affected by the behaviors of your unfaithful spouse and have become aware that your pointer finger is turning into stone,  I urge you to seek recovery before your anger takes on a life of its own.

Getting your eyes and your pointer fingers off of a third party is NOT eating crow. 
Your well-being has absolutely nothing to do with the third party, but everything to do with loving your "self" enough so as to gift yourself with cleaning up your past to set yourself free to fully enjoy the rest of your life.

Yes, it was a betrayal that your spouse chose a Third Party while in marriage to you, 
but yet much, much sadder than his or her behavior, is that 
you went and glued your eyes upon someone who had no respect for him or herself, and when you fixated your mind, body and soul upon this someone else, you thereby gave up doing your recovery. 
That recovery would have restored you and 
made you better rather than bitter. 
That is the dilemma of the third party and recovery.