Hi msnow,
I have looked at your post several times now. I have wanted to respond, but honestly, I remember this phase and it's rockbottom and painful. There isn't a magic bullet to get past this. The only thing I can do is share some things I learned in getting out of it.
I want to tell you a few things and then I will give you a list. Like you, I thought I was in love with the AP. Soul mate, crazy, madly in love. The pain of ending it was all encompassing. It was literally the worst thing ever. And, guess what?
It wasn't unique. The psychology of what happens when you have an EA/PA is almost like clockwork. When you read more about affairs, you will see it's universal.
The person you had an affair with made you feel very good about yourself. Better than you have felt in a long time. Your attachment to them is about that rather than it really being about them. (Yeah, I know, I know...you can tell me all this wonderful stuff about her and you are convinced what I just said was bullpucky)
When an affair like this starts, it starts as often an escape from reality. It lets you be whoever you want to be in your mind. And, the AP is basically fanning the flames with all the ego stroking that they are doing. They make you feel good so you think THEY are good. What starts to happen is a mirroring process. You project a lot of qualities and feelings onto this person as the fantasy/escape escalates. Your brain is flooded with dopamine, creating a euphoria feeling.
So, the snap back to reality is a hard crash. You have been living in a fantasy world. This pain you are in isn't going to go away over night. You basically have become addicted to the dopamine and not having it is going to put you in a very low spot, depressed feeling. You think the answer is to "just get a hit" but it's not. Here would be my suggestions to you:
1. Tell your wife. She deserves to know. This as was suggested by a previous poster will start to ground you because it will be harder to ignore the reality of what this situation actually is.
2. Find ways to replace the dopamine. Do cardio (A runners high was something that really started helping me). Eat foods that help with endorphins. Get sleep. Take vitamins. What you are going to go through in the next several months can be counterbalanced to some degree if you practice good self-care.
3. Work to see this woman for who she is. She is not perfect and your soul mate. She is a selfish woman who doesn't care who she hurts to get what she wants. She has done nothing good here - she's helped you in running your marriage off the road, something that will devastate your wife, and if you have children she doesn't care what is really going to happen to them. This person isn't going to be a good candidate for a partner in any way, she is going to make everything about her and chew you up and spit you out. I know it's hard to believe or see from your standpoint right now, but it's true.
4. No contact. NONE. Block her on everything, do not respond to any time she reaches out. Tell your wife when it happens. No contact means no new hurts. This withdrawal that you are going through has to restart every single time you break contact - so don't be looking at her social media even, that is still contact even if it's not direct. You need to see this woman as highly toxic for you and avoid her like the plague. The better you do that and the sooner you do that, the quicker the pain will go away.
5. Read, read, read. Knowledge is power, and there are specific patterns and issues that you will read about and identify with. Knowing this isn't unique in the least and understanding the psychology will help you get a firmer grip back into reality.
6. When you do confess, do not minimize anything. Try and understand what inside of you caused this. Your wife, marriage, didn't cause this - it was a decision you made probably out of poor boundaries, coping mechanisms, etc. This is on you 100%. Own it. Don't trickle truth, tell the entire thing, sparing your wife from details will backfire on you and hurt her more. Because over time you all will discuss this a lot and she will find the lies. Each time that happens it will be just like what I said with the contact, it will reopen every wound and the healing has to start all over again.