One thing I have gleaned from this discussion is for many the definition of friend seems quite fixed and intense.
I have a core group of (mainly) female friends who I have collected through life - school,university, jobs etc.. and they are my core go to group- the ones you invite to major celebrations, share problems with, meet up woth regularly, talk/dance the night away with. We have supported each other through all sorts - illness, death of loved ones, miscarriages, relationship breakdowns, job loss etc..
But I also have, and have had a lot of what I call "situational friends". People you see a lot of at a particualr period in your life because of a shared situation - work, living situaton, hobby. These friendships can be quite intemse but usually naturally fall away once the shared situation ends but that does not mean they aren't valuable at the time or did not add something to your life.
I find the best way to make frinds it must like the best way to meet a partner - be open to new things, take a chance and accept there will be a failure rate but all experiences add something. We recently went to Boston as Mr Monkey ran the marathon. Accomodation ia Boston is expensive so we linked up with a couple of others he knows through one of his running clubs who were also going out there. So we rented an Airbnb apartment together. On one levle it was functional - we all needed somwhwre to stay, but they were great, we had a brilliant few days and got on well. I doubt we will see them much again (Mr Monkey may go for the odd pint aftet runs woth them) but it was nice to share our break with others and it added a lot to the holiday.