Well, monogamy, yes :)
I tried three years living in a kind of open relation.
My GF was married...he knew me, liked me.
They had two kids and in the weekend we were having excursions all together like a 3-parent family with two kids.
I am sure that was a good experience for the kids as they could see that life is more than just thhe conventional :)
It lasted almost four years and he was my best man at the pagean weddingceremony I had with her.
We considered buying a house all together but then life happened and things turned out differently.
I don know, if I would do it again...propably if I love "her" enough, yes.
For sure it is an experience I do not want to miss in my life.
For the moment I am super happy in a (hopefuly) monogame relation.
My excuses for my terrible typing today...It even does pain to me as linguist..but I typed too much during the day.
Enjoy every phase of your live, because thats what it is: phases :)
Try all you want, but do not hurt anyone and u will be happy.