your going out friends
your online friends
your girlfriend
you best friend
your druggie friends
your study buddy
your fuck buddy
your foodie friends
your boyfriend
your friends you use to make yourself feel better
your friends who use you to make themselves feel better
your backburner friends
your family.
It's only human nature to put people into boxes (in our heads, hopefully) it's how we keep organized. Whether on how to feel, how to act, what's appropriate behavior, what the boundaries are, how fucked up to get, or what to wear even. Everyone has certain people for certain things in their lives. There's that friend you run into from time to time, the one who you're always making plans with that you both know you'll never keep. Then there's the friend (or friends, if you like variety) you call when you just need to get off.
The main problem with this standard categorization of friendships is when people start to shift roles. Pretty soon your druggie friend is becoming more than a friend, and then more than a fuck buddy, and into a significant other. What may now seem like a relationship built on a fun foundation, may seem a little faulted once you take a step back and really look at it. Now I'm not knocking people who date their drug dealers, kudos really, I hope you're getting a discount at least, but just make sure you're not blinded by the initial spot you've scoped out for them
And by that same notion, try not to let that spot over shadow a potentially new place for them to be in your life. On a lighter note, your backburner friend becomes your best friend who you introduce to your study buddy who then becomes part of your family.
No matter what, don't forget those people who are there for you in times of doubt.