Okay, so I'll 'splain some.

Lots of little tripwires that looked very familiar to me, even if they evaded the gaze of the general audience.
FWIW,
MikeT is
a drama queen. While anyone can write a hyperbolic headline -- that's just good storytelling -- his posts revealed this as only the iceberg top.
Somewhere along the line of his life, MikeT learned a trick: when cornered, all he has to do is screech "MEA CULPA!! MEA CULPA MAXIMA!!" & rend his clothes & thrash around on the floor whimpering & pissing himself. (Similar: "thrashing wildly from one extreme to another".) This gives him leverage to control or punish others because he "feels bad." As a public event, the idea is that casual passers-by see this & think to themselves, "Oh, that poor poor man!! He's clearly
trying his best to be a good person & do the right thing!! Perhaps it's the fault of those nearest him -- certainly HE isn't the problem!!" (In
Transactional Analysis, this is a Tombstone.)
Putting on these displays absolves MikeT from taking any actual responsibility, much less needing to make any changes (in himself or his precious preconceptions).
Later it was made clear that the assessment has weight:
He spent so much time thinking about this issue Monday thru Wednesday that it was negatively impacting our intimate life and general happiness.
Basic
emotional blackmail.
MikeT pops in here, & the ploy falls flat (mostly). I figured he wouldn't be hanging around long but REALLY needed to hear some hard truths rather than just good-hearted attempts at sympathetic nudging. A culture of "niceness" encourages failed learning: no Truth is so great that someone can't trip over it, dust himself off, & proceed on as if nothing happened.
And rereading the entire thread, I
still see where his FIRST step has to be creating & defining clear boundaries with Samantha, which means his normal "I'm a terrible person, waaah!!" stuff is NOT useful. To reiterate:
Sam ought to butt the hell out a little. ("Samantha is bothered by the Polyamorous aspect of the relationship")
And IME at least 9 times out of 10, a sudden onset of "STD concerns" is utter bullshit, manipulation under a PC guise. ("Samantha is bothered by ... the idea that Marie would be with other partners, and the risk of disease when I am with them both.")
...as the relationship [with Sam] settles in, I wouldn't be surprised if it was Sam to make moves outside the dyad, possibly without consulting Mike.
Sam is a cowgirl, & this needs to be called out by
someone here.
If there's a major rift because Mike & Marie aren't communicating well? Hmmm... maybe THAT is an improvement path people hereabouts could be encouraging...
miket is having trouble getting to the bottom of why he feels certain things.
I disagree. Rather, MikeT is having problems maintaining the control he felt in the past AND extending his control -- the correct answer to "which way will you go?" is NOT "both ways!!"
MikeT has happily painted himself as the suffering martyr, with his wife "banging other men for free" as he foots all the bills. The fact that this suddenly leaves Sam out of the frame suggests he's either manipulative or insane.
Maybe MikeT brings in a little more income, but he's also off with Sam at least occasionally, therefore not carrying his weight at home, & maybe OUGHT to be paying a few dollars more.**
My Dad was VERY opposed to Mom working out of the house, though his job was/is highly seasonal (fulltime only 6-7 months/year, no winters). However, Mom waited until autumn, then pointed out it'd be nice to pay heat bills AND have plenty of food AND buy some nice gifts for the kids... & Dad agreed to let her take a seasonal job. We skated through winter, & Dad grudgingly admitted that not worrying about bills was VERY much worth cooking his own dinner sometimes.

However, that was also 1971

& seriously "po' white trash" rural, so I'd have to call the attitude anachronistic at best.
Marie & Mike both profess wanting to stay together & maintain the status quo... but to ALSO explore nonmonogamy in fundamentally conflicting ways, & without doing much to determine what it is each wants & they want as a dyad.
Are there resources for men to unlearn patriarchal beliefs?
It's almost more of a "12-step" thing. First, there's seeing the possibility that
someone could change... then that ---I--- could change... then that I ---want--- to change... then learning what needs to be changed... then doing the actual work... & it continues on.
If MikeT doesn't feel he needs to change, that he's always in the right (no matter how badly this might make him feel), then (short of zapping him with a Taser from time to time) there's very little anyone can do about that.
________________
** -- a strong suggestion: if each of the couple is putting 100% of their paychecks into a joint account, STOP THAT RIGHT NOW. I've never seen that end well.
When we had a four-person household, we figured out what it cost to pay the mortgage, & the utilities in deep winter, & have a small repair reserve... then factored in cable TV & washer/dryer & restocking basic foodstuffs... bumped it up a few dollars more just in case... then split the number four ways.
The resulting number was significantly less than area rents; we voted to give the least-employed of us a break, each paying like $20/month more to help her out, putting her on a more-equal footing.
As a result, we all controlled the space about equally, & all felt about the same responsibility to the house. Sometimes we'd even bribe each other to take over certain chores. 
Take what's left & bank it in your private accounts. Use it to be individuals.