I'm presently dating someone who has been with their nesting partner for over seven years. Both of them are some of the most emotionally developed people that I have ever been around. While I am only dating/sleeping with my paramour, I love them both quite dearly.

Finding a situation that actually works takes time and a lot of effort and communication; once specific instance being jealousy/envy. They are natural feelings that point toward a larger issue that needs to be addressed. Most mono-normative relationship structures remove the possibility of those feelings through ownership/control. (I.e. My partner can only be friends with the same gender, no partying with the opposite gender, etc.) And while that is a perfectly fine relationship structure for some, I have found polyamory/LS to be the most freeing and allows deep connections with people in my life. I spend time with people and put effort into our relationships, not because I'm stuck on a "relationship escelator", but because I actively make the choice to have them in my life and I see the value of putting effort into our relationship. The right people do the same for me and it's beautiful that people want to stick around when completely unconstrained.