Also nature. It's clinically proven that living your life surrounded by barren concrete fucks you up.
People like having pets and growing houseplants, just cuz, and both have been shown to do a lot of good, mentally. But we really should be bringing nature into our cities much more than we do right now.
Aside from worsening the mental state by deprivation of nature, it also is more vulnerable to flashfloods, the heat is much worse in summer and the air quality is worse all year round.
I live near seattle. A friend who grew up in texas visited recently and he was shocked at how many trees were around in the city, and at how clean the air felt
You're right, it's not just "people." What I mean is we need to focus more on our relationships, and on being around the people that make us happy, and less on the things we think will make us happy.