Let me ask you something... please choose from this list...
1) The lying, sneaking around, secret-keeping and constant need to cover your tracks and hide your double life
2) The joy of having sex with someone else while telling your spouse and kids you are out doing something else really important
3) The loving feeling you get when you think of the AP's spouse or yours and you realize how much they don't matter and how easy they are to fool
4) That sense of "I'm a good person" that naturally comes when you are sexting your AP while your spouse is sitting just across from you
5) The knowledge that nothing in the world could possibly come between you and the AP since your relationship is built on betrayal, lies and "mutual use of each other"
Of the five topics above, which one do you feel makes you miss this love of your life the most? Which one is your spouse not currently fulfilling for you that you simply can't stop thinking about or living without? Is there perhaps an STD that you wanted but never really achieved?
Okay, I'll stop now, I really didn't mean to be harsh, or snide, but I do want to be real. Because as harsh as those things might be, they are nonetheless very, very real. They are the things we need to keep in mind when the "the fog comes rolling in" and we start to fantasize about the escape the AP and the affair offer us.
I think, for most people, the affair represents this fantasy, this "escape" from the pressures we face, from the shame and bad feelings we carry, from the negative viewpoints we hold of ourselves, from life, from everything.
When your AP reached out to you, how did it make you feel? I mean, really this time? Were you excited? Curious? Did your heart skip a beat? Were you suddenly happy? Intrigued? Was part of you disappointed that she said it's still over? If she had said, "My god I need to see you and I need to see you now because I love you so much and my heart just can't live without you", is that something your heart secretly wanted to hear? Do you still want to be wanted? Do you still want the excitement? You still want to feel loved and desired and special? Do you want new options in your life, a new chance, a new path?
You need to be really honest with yourself about what you are actually getting from all of this. And yes, I know, you probably are already aware of all these things, the real question is, do you know it in your heart and soul, or just in your head? Is it still just lip service to yourself?
Thoughts of the AP go away (very slowly, over time) as respect for yourself returns. Right now, there are needs, your needs, that cannot be fulfilled by you for whatever reason. You need them to be fulfilled externally. And external validation is a losing game, because your intrinsic self-worth will never be enough for you (unless something changes), and external validation is not something stable that you can count on. SO what to do?
Well, you need to be able to fulfill your own needs. You need to be enough, for yourself. You need to stop living as a victim, as someone limited or defined, and instead gain a sense of self, a sense of pride in yourself and in who you are, and realize that you are someone of intrinsic value and worth. It is good to love others and to want them in your life, but it is not good to NEED others. No one can truly love someone else unless they love themselves first, and that is the part you seem stuck on right now. At some point, you need to get so sick of being this unhappy and unsafe person, that you actually make the changes needed. When you wake up and think to yourself, "If I am never in another relationship again, that's okay, I will be happy and I will be okay".
My advice? Try not to focus on your marriage for now. To be honest, in this state of mind, it won't help anything anyway. Don't misunderstand that statement as "give up" or "leave", don't do that! Rather, stop trying to control or change the relationship, that is a failing path. Focus on you. Focus on who you are, who you want to be, and what is acceptable and unacceptable in your life. If you have a daughter (and if you don't, pretend you do), and that daughter was in a relationship with a guy who was treating her the way you treat your wife, how would you feel about that? If she was acting the same as your AP, how would you feel about that? If either of those scenarios makes you a little angry, then stop and turn that around. Why are you allowing it in your own life? Why the different standards?
Breathe. Keep going to IC. Do something every day just for yourself, something good, something positive. Even something as small as letting someone in the line ahead of you at the store is a good start, and when you do, say to yourself, "I am doing this not to feel loved and appreciated by the person I let in front of me, rather, I am doing this because I take pride in being someone of good character and quality and because I value my own sense of decency and the value of others in this world". If you let someone in line and then tick off a checkbox saying, "See, I did it. Now others should see me in a better light." then you are doing it wrong.
Best of luck to you. Give yourself time, give yourself healthy boundaries, give yourself a break, and give yourself permission to be unhappy or uncomfortable for a while not defining yourself as a bad person.