Like, you aren’t necessarily next door neighbors. You’d have to take the streetcar or bus or commuter rail some distance to go meet your friend. You can’t text “sorry the train is 30 minutes late”, because no cell phones, no internet, no tracking buses or trains on your smartphone. No payphones or landlines.
Letters are only for those cross-continental, cross-oceanic relationships. If you live in the same city, then well you’d still have to meet in person cuz it’s not the digital age, no doomscrolling social media and sending texts and memes.
I feel like those were the days where you could have true friendships in society, not “having friends to send memes”.
If this is about that period of human history where we had long-distance transportation (ie railroads) but didn’t yet have mass communication infrastructure that isn’t the postal service – so 1830s to 1860s – then I think the answer is to just plan to meet the other person at a certain place every month.
To use modern parlance, put a recurring meeting on their calendar.