My triad for the tiny little time it existed (Feb to Aug of last year) worked beautifully. It broke up due to outside influences but it was a kind and thoughtful friendship between my husband my secondary and and me. They often did things together without me. We all played music together. We shared meals together. I spent time with my secondary at his home and the rare occasion my husband went there as well though mostly they spent their time together on outings and building things. It was quite harmonious for the most part. I don't have that now but things are ok. I am still free to come and go as I please. I have never contacted my former secondary as I felt crushed when it ended not even maintaining a friendship (his choice). I would certainly hope another relationship can happen again but it will be hard to repeat for me. My primary relationship almost came apart when the other relationship ended but we seem to get stronger now and I appreciate him more than possibly I did before. Sadly he misses him sometimes and does wonder why we couldn't maintain the friendship. Maybe someday we'll see him again but I don't know... I know I will not be the one to seek him out.
I think when it was successful was when we all did things together like a family. That's what it felt like. I hope you can find some peace in what you are looking for.