Here is my weigh-in on the question, and my reality when an affair blew my relationship apart. I have not done this yet, so it may be a good exercise for me!
Confusion. First, I could not understand what I was hearing. After being with a man who made me feel like his world revolved around me for 10 years, this made no sense. I thought my ears must be broken.
Disbelief. I could not even wrap my head around the news (most days I STILL can't believe that this really happened). I struggled to fit this into some compartment of my brain that made sense. There just wasn't one.
Shock. Immense shock. This lasted for quite some time. I had to drive a friend to the airport that day, but don't remember most of the trip. I have blackout periods from that day and the next. My nervous system went into complete overload.
Panic. Sheer and utter panic. I had to face the reality that my relationship was over (he told me that before walking out on me. At the time I believed this was true. It actually is not). As well, I had to face the terrifying thought of moving, where would I live, and how would I survive. I spent the afternoon in an office photocopying my mortgage paperwork so I would have a copy of my assets. My brain went into a complete panic tailspin.
Desperate sorrow. I could not believe this was happening to me, and was inconsolable. I spent time on my girlfriend's living room floor shaking and unable to stop screaming.
And this was all on the first day. This was then followed by:
Severe physical reactions: being unable to eat (I did not eat a meal for 6 days and almost passed out at work one day), being unable to sleep, exhaustion, and very bad stomach upset. Somehow not eating for 6 days did not stop the unpleasant reactions my stomach had to the news :( I began to exhibit PTSD signs, not being able to be out of the house for too long. I walked out on 2 social events because I HAD to get to the safety of my house.
Rage. Once the shock started to wear off, the rage set in. Overwhelming and uncontrollable rage. This was also terrifying to me, because it was not who I was as a person. I sent email after vicious, cruel and blinded-with-rage email to my partner. The rage was quickly mixed alternately with a sadness that cannot be described. This see-sawed back and forth for at least the first 3 months. It was terrifying, and made me scared for my own sanity. I finally went on antidepressants to try to level my moods out.
Grief. This experience can be closely related to the feelings of immense grief. I recognized that feeling of "NO-this CANNOT be true, please someone tell me that this is not real!!". Having lost both of my parents at a very young age, I have had experience with not only grief, but grief for something that "shouldn't have happened". This felt the same to me. I was grieving, but grieving something that seemed so unnatural and WRONG to me.
Betrayal. I think out of everything, this was the most devastating and overwhelming. To this day it is still what I struggle with the most. The feeling of being betrayed by someone that I loved, trusted and thought would NEVER EVER hurt me to such a degree was absolutely devastating. I was crushed beyond ability to convey. I doubt that I will ever be able to express to my partner exactly how this made me feel. There are no words to describe it accurately enough.
Jealousy. This set in around the 3 month mark. I had an uncontrollable and dismaying level of jealousy, and could not stop obsessing over what they had done together, what she looked like, the whole fucking ugly 9 yards. This also caused me an immense amount of distress, as I don't think that is who I am as a person either. The jealousy also admittedly caused me to become turned on thinking of him with another woman-I know it is sickening but I have read that this happens. Of course to me it was absolutely sickening. So I wondered what was WRONG with me :(
Abandoned/feeling alone. We were separated for 3 months, and through all of the ugly feelings, I felt so alone, and the yearning for the life we had had was overwhelming. It caused me so much sadness. I felt abandoned by a partner that I always thought would be there for me.
Insecurity. My feelings of self-worth were completely shattered. I eventually found out details of the physical relationship and this hit me very hard. I could not imagine my partner doing some of those things with another person, and this caused me an indescribable amount of distress.
Suspicion and mistrust. This is the stage that I am in now. It has also caused me a huge amount of distress because I am suspicious of everything that he says and everything that he does, even though he is trying hard to reverse this. My trust has been damaged severely.
The list could go on forever. Even having lost my parents at an early age, I think this by far has been the single most traumatic event of my life. The best news that I received during this time was from my sister. She told me that I would NOT be making any decisions as to what I was going to do for at least the first 3 months. This took the pressure off of me from feeling like I had to decide, and helped immensely. I was barely able to function as a human being, so rational thought was not happening. Don't expect it.
I was also told that this would probably be the most important time in my life to put ME first. I took that advice and took care of myself as best I could. I hope you take both pieces of those, and continue to get through day by day. This is going to be a LONG process. You can't rush it, so take your time. Wishing you much healing.