Chances are busting her and confronting her won't change anything. Chances are going to the pastor and telling him (and then having a meeting with her) also won't change anything. More likely than not...at this point...she'll continue the affair regardless of getting caught.
Collins' obligation is merely to speak the Truth. He must hold her accountable for her sins towards him and God by pointing them out and asking her to stop. He can't judge or condemn her but he is responsible for letting her know he is aware she has a huge plank in her eye and she needs to remove it. If she refuses....it's his responsibility to speak to his/their pastor who SHOULD (they don't always unfortunately) bring the wife in for a serious talk. She should also be suspended from any leadership positions.
Whether his wife removes the plank or not isn't his obligation. She's responsible for that. He only must answer for his failure to cleave to his wife and speak his Truth to her (whether she agrees or not).
Although we must never pass judgment on anyone, because we do not know their heart or all of the hidden reasons behind their actions (she may be mentally ill), we must always bear witness to the Truth revealed by Christ, because it is that Truth which will set all of us free from judgment ( John 8:32). We have all fallen short of the Truth from time to time in our lives but adultery is a big one and who else is more responsible for helping his wife understand God’s will is NOT for her to pursue this route than her husband such that she will be better able to stand before Him at the final judgment. Christian exposure and church discipline is an act of charity, not cruelty and not punishment.
If she doesn't come around immediately...God should continue to work on her heart and her conscience. A true Christian can only deny His word for so long.
btw...busting her, confronting her and discussing this with your pastor soon also leaves open the possibility that maybe you can get her to choose to stop this destructive behavior BEFORE she actually has sex with the guy. Earlier today I speculated that because she wanted to have friend zone sex with you the other day might be an good indication she isn't sleeping with OM .....YET. Emotional affairs are hard enough to overcome....but stopping it before it goes physical (and into adulterous) would be a huge blessing. Conflict avoiding might mean you miss this opportunity to potentially stop this before it crosses that line.
The internet is 90% complaining and entitlement and I hate it because I deserve better!