I have a long history of joining others for Thanksgiving or Christmas. As a teen, my grandmother worked full time, and my mother lived either two hours away, or seven once she moved to Missouri. Grandmother adopted me in the 10th grade, after a series of abandonings by Mother. The mess Mother had made of raising us had been widely seen and known in my small hometown, so it was easy for me to put the sense of shame behind me since it was no secret, nor was it anything a kid could do to fix it.
It was more traumatizing to live with a grandmother whose house was falling down and who hoarded trash and mess and was thought eccentric because of it. I spent as much time as possible at school, at church and youth events, at band practice, in choirs, in school plays, and eventually, working a retail job after I was 16.
There were about five friends who treated me like family, and I was welcome in their homes any time. One was a bandmate across the road who was two years older. His mother was divorced and raising four kids on her own, working full time, but she went out of her way to help me, over and over. She is the one whom I posted about a couple of years ago, a foster mom to me, dying of lung cancer after four bouts of it. I went back to Little Rock to attend the funeral. I went to all that detail above to say, her love was true pity. I was a gawky, nerdy, acned teen, with insecurities, needs and talked too much. Her pity wasn't some faux virtue, some check-the-box to say to herself that she had helped the poor. She cared. I have no idea how many times I ate at her house. She was like Jon's mom from Garfield, "eat, Eat, EAT!" Thankfully, she was a wonderful cook.
I'll spare you the others, but I was practiced at making friends into family by the time I was an adult. And, after I left my hometown almost two decades ago, I was far from family or friends and gathered with new friends where I lived in New Mexico, Alaska, or Connecticut. Those always were fine. I wasn't treated like some pitiful, lonely thing, and I wasn't.
However, to bented's point, my neighbors and friends here are not the same. There are a few I eat with, but I've learned not to accept for holidays. Things are different then. Their kids are home and I just become an outsider. They are adult children, but make no attempt at conversation and have no interest in knowing me or becoming a friend. So, even though I'd gladly join the friends on their own, joining them with a family where I'm the only non-relative there makes me feel stigmatized.
I will say that some of the parents of my friends back home would have multitple non-family guests to where it was a true potluck type of affair, and we would all bring a dish and be in good fellowship. There would be widows, almost-orphans, and any visitor or someone from abroad who might not have family to join. It was a warm hospitality.