I have lived long enough to know there's at least 3 friendship types.
There's the friends of geography. So long as you live/work in the same area, you can be friends. Maybe not after you leave the area.
There's the friends of age and stage. So long as you are in the same life age moments (student, pregnancy, whatever) you are pals. Maybe not after you move to the next life stage.
There's friends of the soul. Friends like this are more rare, and no matter the location, age and stage, whatever. You click on a deeper level. They can leave and come back into your daily life or never daily again but just a call or a card -- and you pick back up like you never were apart. I am lucky enough to have married one, and then I have another who I have not seen in person since I don't know when. But I know it is SUPER rare to find TONS of this type! So I remain open but do not expect EVERY friend to be this type.
All friendships matter, and give your life colorful experiences that enrich you. I'd enjoy them all regardless of friend type and just be open for the new folks that flutter into your life next.
My post college friends that I like best I made via church and volunteering. Work not so much. I was a telecommuter.
GL!
A.