> That is a complete red-pillesque reductive explanation that I'd expect to hear out of a MGTOW style community
Precisely, I didn't mean for that comment to sound like an endorsement. Maybe I should have used a "/s" but it's not actually sarcasm, it was just meant to illustrate what some people believe. My bad. From the little I have seen, MGTOW fall into the trap of believing possessiveness is only applicable to women, along with other stereotyping misogynistic beliefs.
In case I actually gendered the explanation, I did not mean to. Either partner can be possessive. I do not know whether there are studies on which direction it happens more often.
> Intimacy happens at more than just physical the physical, and most people reserve some types of intimacy (physical or emotional) for their significant other. When you cross the boundary of intimacy you normally set for people other than your significant other with someone else, that can easily be interpreted as disingenuous or betraying to your SO.
The point is that each partners boundary is a personal thing, it may be agreed upon in a couple if it was discussed in advance and it can be shifted afterwards. And if it is discussed, it may be set in the same place for both partners or not. But by default, if it is not discussed, it is likely to be different. And people are likely to judge others assuming that everyone's boundary is in the same place.
The boundary can be set anywhere but it is important for each partner to know the other partners boundary and decide whether it is something they can live with or not, in which case it is better to find someone who is a better fit, otherwise the result will be resentment, betrayal and conflict.