My own take is it is some sort of LBS fog where the LBS can't bear to blame their own spouse so they project it onto the OP. It may very well be that the OP supports the MLCer, as one would expect a partner to do, but I think that these MLCers are so out of control that no one really can control what they do, not the OP, not the LBS, and probably not even themselves. And attempting to control others is such a big part of MLC for many of them that you really have to look at them as the ones in the driver's seat. Or at least that is how I look at it.
I think like many of the spectrums on this website this is another area where behaviours are on a 'spectrum'.
At the far end we have the LBS blames everything on the OW, all the MLCer's love and affection is buried, if we could just get rid of the OP then he would come running home...we shall call this 'pink tutu' syndrome.
On the other side you have LBS anger and rage. Everything is solely the MLCer's fault, they are to blame, they completely changed, they flipped out...they do it all because they are evil. We shall call this 'monster hunting'.
The truth as always will lie somewhere in between, and where each LBS is will vary on the spectrum both now and over time.
So to say that the OM/OW has no influence over the MLC is impossible. All partners/family/friends have an influence on you. People you sleep with definitely do. The OM/OW is invested in this 'relationship' for what they get out of it. Be it money, adoration, career advancement, or just wanting to win. It doesn't matter. They will have a voice that pokes at the MLCer and urges them to do what they want and what they have a vested interest in. Same as a married couple do, though probably a bit more selfish by both of them.
The MLCer will have a choice. They can feed the angry demon raging inside of them, and say ''Om/Ow is right! I deserve this...'' and go after it using the AP encouragement to feed their own desire. They can think ''I am not really sure, I think OM/OW is just jealous'' and maybe drag their feet. Or perhaps they decided OM/OW has no say in the matter so they just nod and listen until the whining/b!tc#ing gets to much...so they inch the progress along just enough to get them off their back.
It is to complex to just say ''it is all AP fault'' or ''it was always my MLCer's choice''. It is their choice ultimately, but their heads are a foggy mess and the closest person to them at this moment is the AP. The AP does have influence over them, and does ultimately guide or nag their decisions to some degree. Some MLCers will see that for what it is, some will go with the flow, and some will have fights to tell them to back off. That is probably due to a MLCer's individual nature and how far they are still in the limerance stage (or whatever term you'd like to use for schmoopie ville).
You know this is MLC when you have played emotional hot potato with a pair of crotch-less tights.