I’m here to tell you, this is perfectly normal behavior from someone in your position. The reason your mind wants to go “pain shopping” (which I agree is a completely fitting term), is its lapsing itself back into a cycle of routines. Routines are comfortable because we know and expect x -y – z to happen.
Work + Work + Work = Pay
Pay + Pay + Pay = Reward (House, Car, Vacation, etc)
That way, even though we may not like the work, we know the incentive (which we do like) which causes us to do the work. The same can be applied with a relationship. Before anything happened, all was well and life was progressing. Both of your routines coincided, and you therefore formed your own routine. However, once something (cheating) interfered with the routine, it caused a lot of pain and you stopped progressing.
THIS is the new cycle your mind is set in.
Good + Good + Good = Pain.
So in other words, when you now get to the point of “good,” your mind reverts back to the last time something was “good”. After the infidelity the next step is “pain,” so you go pain shopping of your own volition. We are creatures of habit and unfortunately, when something like this happens, there are few ways to really fix it.
Counseling, communication, forgiveness, acceptance, or separation are really the only options. The best way is through therapy / couples counseling. As the issue (pain shopping) lies in YOUR behavior because of HIS actions. It’s like burning your lip on a cup of coffee. Your mind and body control everything. If you burn your lip, you take the cup away. Blow on it. Give it time. And then enjoy your drink. What you’re going through is that you want a drink of coffee, but HE’s controlling the cup. He can try to help, but you still got burnt. You have to learn how you BOTH need to function so neither of you get burnt. I hope this makes sense and I didn’t lose you too much.