I'm a woman in my mid-20s. In the last year, I've noticed that a number of my core friends have begun to exhibit traits and values that I don't really identify with. I do my best to show up for them, but when I go through a hard time, they don't seem all that concerned with my well-being. However, I have a history with these people, so I feel I owe them my loyalty.
The fact that something has gone on for a while is not reason for it to continue. Take the long "history" of people eating people — dating back 100,000-plus years and still occasionally (though criminally) practiced today. These days, sure, there are restaurants that specialize in "traditional fare," but their entrees tend to be roasted leg of lamb — as opposed to roasted leg of Bruce.
Likewise, the "because history!" argument for staying with a friend ("We've been in each other's lives for 17 years!") is not reason to braid each other's hair and skip off together into year 18. "History" in the friendship context often means having lots of shared experiences (especially misadventures like ending up side-by-side in the back of a police car after getting caught shoplifting at age 10).
Some of these "historical" experiences — like your friend being there for you in tough times — can make you feel you've got an unpaid bill to work off, endlessly indentured friendservant-style. But do you actually owe them? Doing good for you probably did some good for them.
Research by psychologist Sonja Lyubomirsky finds that two of the most effective ways we can make ourselves meaningfully happier are regularly "practicing acts of kindness" and "nurturing social relationships." You might also consider that a friend who helped you surely did it by choice — not because you held her at gunpoint and demanded, "Listen to me sob about my ex for 26 hours straight!"
However, because we're prone to feel guilty asking ourselves the legit (and healthy) question, "Hey, what do I get out of this friendship?", we often end up populating our lives with fair-weather friends: there for us whenever they're in need. Granted, friendship is not always 50/50. However, if the give and take balance is generally 5/95, your friendship is less a friendship than a usership with a nicer name.
We tend to be hard on ourselves if we end up with a collection of toxic friends — or friends who aren't bad people but just aren't good people for us. Though we believe we carefully handpick our friends according to shared values, attitudes, and interests, the formation of our friendships may have more in common with closing our eyes and throwing darts than with some Socratic inner dialogue on a potential friend's merits. Psychologist Mitja Back finds we often form friendships through "mere proximity" —like being next-door neighbors or being assigned to sit next to each other for a semester in a college class.
Understanding this might help you be as discerning about your social world as you are about your physical one: "Um, maybe that house next to Acme Turn-You-Radioactive Chemicals is not such a steal." This is vital because the sort of people you're frequently around shapes who you are, seeping into your thinking, habits, and motivation. So, it's important to have a "core" group of friends who share your values: the bedrock principles underlying the person you want to be (your ideal self).
These friends, simply by being who they are, will motivate you — monkey see; monkey do! — for example, inspiring you to work harder or smarter. Also, at times when you see nothing but gloom and doom, they'll pop up all human flashlight to point out everything you've got going for you.
This isn't to say you should exile every person in your life who doesn't exactly share your values. Just be sure they're in your life not because they've been there for eons but because you choose to keep them around: They're fun; they share your sick obsession with the 1972 Pinto; or they need you and you feel good giving to them (though they can't give back in equal measure).
If you decide to part company with opportunistic, emotionally toxic "friends," avoid any temptation to take the "Off with your head!" approach — like abruptly disappearing without explanation. This is mean, and it can lead to ugliness and ostracism by mutual friends and acquaintances — as can "constructive" honesty: explaining that you can no longer be friends with such selfish users. It often pays to fade: Simply become increasingly less available...like for those amazing opportunities to devote your entire weekend to helping your bestie move — in exchange for a pepperoni and dust pizza they make you eat in the back of the U-Haul.