This is some really solid advice. My fiance and I are not poly, but we're what you might call poly adjacent. We have a lot of friends who are and have been to lectures on the subject and such. Around the time that marriage for love (and also separating by nuclear family as the default), or having to find your soulmate became the primary reason for marriage it also seems to have pushed the notion that your partner should also be your best friend, your lover, your business partner, your therapist, and co-parent. This, to be blunt, is a fucking insane thing to expect of one other person. IF you have that with someone, great, amazing! But it's super rare that you find a person who can be all of those things and do it effectively. One of the things that I think monogamists can learn from the poly community is that maintaining multiple relationships does not dilute your feelings. What it actually does is allow you to focus on what is strong in your relationship with each person and not force you into interactions with them which they may not be interested in or equipped for. Humans used to live much more communally than we have since the early part of the 20th century and I think we have abandoned that to our detriment.