(wishy-washy, unverifiable emotional pseudo-psychology follows)What I mean is -- you do not need to have a partner and your own kids. There are all sorts of families (macro and micro) out there that can benefit from us.
On the micro side: you can allow yourself to be included in your best friend's family, you can allow friends to become close enough that you know they'd be there if you were sick and vice versa. You can think about lonely older people who you feel kinship for and be brave enough to offer them support. You can sometimes convert former romantic relationships into trusted friendships, and you can widen your romantic ideals to include joining a single-parent family that already exists.
One step up: you can treat your wider friendship circle like a family, believe in them like you would your family.
On the macro side of things: you can join a community and allow yourself to be absorbed into it as someone of significance; you can help people find their people. Introduce people to other people; be the reason other people have people.
All of these things require a kind of bravery that deserts most of us at some time, and obviously a kind of comfort with other people that not all of us find easy at all, but really any step you make to try to build a "family" is better than no step.
When you're young you don't need it and you forget to look for it, because new experiences outweigh family ties. When you're old you need it and it is harder to find.
When you're 35... this is the time to enjoy the thrill of being brave and seeking real connections with a mature mind, and allow yourself to think of it as building family and significance into your life.
I managed some of this -- a real social life, real connections -- for a long time from the age of 33[0], and then the pandemic has undone a lot of that; people have scattered. And if all of the above sounds preachy and patronising it is because it's really all I think about again -- how do I get that back, at the age I am now?
[0] "Lord, to be 33 forever"