LivinginGrief and Lefty,
I have to address this statement first because as a WS that was part of a double betrayal the following statement really makes me angry.
I imagine that your WH and his AP had a bit of a giggle being able to sneak around right under your noses.
Never once did I have a "giggle" about sneaking around right under my husband’s nose. Never. After finding out, my husband did assume this was the case. He had this Machiavellian image of what the affair must have been like. With time and a lot of work, my BH is able to believe that isn’t the case.
I honestly wouldn’t have been surprised if I had been diagnosed with an ulcer at the time. It was very stressful. Always on alert, always trying to act act normal. Always trying to read something into everything the other couple did. Acting a complete fool and doing things that degraded myself in the name of "stollen moments".
It is constant battle between feeling guilty and taking advantage of the friendship in order to spend more time together. But in the end, what was mattering most was getting my needs met, which meant not dwelling too much how messed up the situation really was. At one point I had convinced myself that we could all be friends after things came to light. I had convinced myself that my husband would be relieved to be able to move on and he would be able to hang out with us. Clearly I was delusional, but it goes to show you just what lengths we can go to lie to ourselves that everything isn’t as serious as it is.
The real life, actual consequences were so far from my mind that I never even considered them other than divorce as a general concept.
I’m not sure what could have been going through your WS’s head while you were all together, but I understand wholeheartedly how difficult it is work through a double betrayal, especially when it is a best friend. The two people that you trusted the most in the world have hurt and betrayed you.
With the AP being a neighbor, moving is most likely the best option to heal. Severing those friendships for good is necessary. If you have a good candidate for reconciliation, allow yourself to express your pain for both betrayals. You will most likely start learning of things or ways they would "connect" that need to be processed, be it songs, looks, secret words, etc (I had to clear out a lot of songs from our playlists).
All in all it is weird combination of guilt and compartmentalization. How much digging into the "why’s" has your WS done? A lot of figuring those out will have to do with what they were able to tell themselves to cross that boundary. How they justified their actions will be telling in how they were able to be around both you and your AP simultaneously.