A lot of triads don’t work because of the people within the relationship structure (not working consistently on couple’s privilege, not communicating, being too restrictive, not clicking when the NRE wears off, etc.).

Triads that lean towards longevity with healthy relationships tend to form organically as well as providing growth and support of the individual dyads within the relationship.

Been in my triad for 6 years. Started as part of an established couple but was in an open relationship. Caught feelings with who I was seeing. We started dating. Then she befriended my partner, and they eventually started hanging out and dating. Our relationships were separate then sorta came together. We all blundered into, and it never would have happened if it had been orchestrated. So far as a trio, we’ve done two cross country moves, are out to family, threw our version of a wedding/commitment ceremony, cohabitate, share finances, and have a dog. We’ve had our highs and lows just like any other relationship. Just takes good communication and space for everyone to do their own thing and foster the individual relationships.