As I get older, I'm becoming more aware of the varying levels of friendship. I think these are the types:
1. True friends. It doesn't matter how often you see or communicate with these people; you always have them. We have maybe 2 to 8 of these people.
2. Former true friends who have faded into acquaintances (see #4-#6). Usually a falling out somewhere along the way that could never fully be recovered from. We usually have 1 to 3 of these people not counting breakups.
3. Friends you don't see enough or get beyond surface level conversationally enough to become true friends. These are usually people who are fun to party with or see when you're traveling to their city only, sort of like service industry friends who only ask you to hang out when they're at work. This is usually the largest intimate group and the best source for dating prospects and future true friends; probably a good 10 to 15 people.
4. Friends you keep at Facebook distance. Most prominently, people who weren't true friends in high school or college, but think you live an interesting enough life to follow via social media. This is the first stage of fringe friendship and includes all the people you met before you became the exact person you are today (e.g. change of city, marital status or career).
5. People you follow on Instagram who like your photos (and you like theirs) but you don't actually hang out with or know them. These are people you'd like to date or be friends with, but have enough people in groups #1 and #3 to keep you from needing it to be more; also a good source of #6 folks.
6. Frienemies. Often people in group #2, but often people in group #4 who you simply haven't deleted on Facebook.