Some really good points made. Thank-you everyone for your thoughts.
LA44, You could have been writing about me and my xAP. It should never have gone on for as long as it did. But it did. Why? Because, essentially when you have two emotionally weak and cowardly people, and you put them together, they start relying on each other to keep standing. Phrases such as "You help me function in my real life" and "Looking forward to entering trying/xAP world tomorrow" were very common during the A. There was no hiding that it was a relationship of convenience on both sides, BUT as time went on the convenience went into dependency and fear of living REAL life without that person that makes things so bearable. That person who allows you to continue living your "crappy" life without really having to take any real risks or make any sacrifices. In other words ESCAPISM.
I believe, during some point in a LTA, the woman (mostly more than the man) will want to have more security and stability and will pressure the man for this. He will realise, actually, I already HAVE the wife, the kids, the home, the car. I don't want that with YOU. I want the FANTASY with YOU. I want the ego stroking and the unlimited sex. He knows full well, that if she becomes his WIFE (which is what she's asking for) he will be where he is now. Please do not see this as a flippant and fleeting comment. It's what I've gathered from my own experience and from my extensive research and reading. This does not mean this is the case in ALL LTA's but in very many. She's invested the time in him and now she needs something to seal this and validate all her energy.
The factors and themes that come up again and again seem to be the availability and accessibility. An A needs to be "fuelled". I fuelled mine during working hours. It was an 8 hour long day of mutual ego massaging. It was enough quality time to become intensely emotionally ravelled up in one anothers lives. So, the jobs that people have within the dynamics of an A are important in relation to this.
In my case, xAP had a job where he sat alone all day in an office and basically chatted to me. He was a director in a company and had zero motivation to do the work he was doing. He hated his job and was stuck in a war-torn country with bombs going off around him on a daily basis. My H was at work all day and I have full time domestic help which again created the availability. It was pathetic and we acknowledged how pathetic it was but still felt compelled to do it. Why? Because we could and we didn't see why we shouldn't.
Another theme seems to be the distance. It would appear a lot of LTA's are also long distance. Therefore reducing the probability of getting "caught". No chance meetings, no unexplained absences, no having to make regular excuses. The risk appears lower and therefore easier to justify (it was for me). "I'm not doing anything wrong" mentality.
The irony in this situation is this; the distance would cause frustration as the bond became stronger(time differences, lack of opportunity to "meet" etc). The frustration lead to many disagreements and aggression. Surely, this would be too much hassle and it would be easier all round to end the drama? For some reason, the "challenge" now becomes the centre and the focus of the relationship.
One other theme that is very true for me at least and for many in this thread, is the fact that the AP becomes part of your daily life. They are intertwined with your daily activities, what you had for dinner, what activities the kids have that day, what movie you watched last night.
For two lonely and desperate people, that type of attention can lead to distorted thinking. The importance of mundane activities is magnified and given relevance. This is important for someone who already "hates their life".
What makes an A go on so long? Essentially the fact that it can. Sounds simple enough I know, but that seems to be a universal answer. It goes on because it can.
Note, NONE of the themes have any direct connection to the BS. It has nothing to do with them. The conditions present that allow a LTA to go on for as long as it does is ALL about the AP's. The BS is just another "compartment" in this double, twisted, deceitful life that the wayward lives for so long.