hi hhh, well not that I'm so knowledgeable about it, but I think there's that line of difference between boundaries and ultimatums. But in a way, setting boundaries is in itself an ultimatum that says "respect me at least in this basic way" with an implied "or else ...".
GAL simply is living in a way that shows that if you had to (not that you want to), the "or else" is a pretty fulfilling alternative for you. You are happy, complete, and have lots of good things in your life.
In a way of speaking, the "Gucci way" puts the shoe back on your foot. It's simply showing the WAS that there's a consequence to what they choose. No matter how much you may love your spouse, and how much you want the M to work out, it's untenable to just let them get away with murder; if they get the benefits of having you available while they waffle and cake eat, why stop?
There are obviously differences between men/ women, but I don't think this is necessarily one of them - regardless of gender, exclusivity in a monogamous relationship is a desired goal. The way of dealing and reacting to transgressions ... well yeah men may have more of an issue.
Your H may start to feel unwelcome and unexpected reactions if he ever thought there may be a threat to the position of having you around as an ever-available option.
Caveat of course, is that this is just my own limited, inexperienced take on the question you posed. Take care
Me 42 W 39 Married: 11 Jan 1998, T: Since 1992 First Bomb: Sep 2007 Confirmed A/OM: 4 Nov 2007 Kids: D10, S5 Reconciled and together again after (alot of) time and heartbreak. 3rd kid, S, born 2 Jan 2010.