Friendship should be a two-way street, but we've all had those "friends" who just can't seem to reciprocate. When you're around them, you feel drained rather than energized. They ask for favors, but don't return them. They might even insult you or your other friends. They're toxic. And yet...we keep them around.
Sometimes we don't realize how damaging these toxic friendships are to our own wellbeing. We think we're being a good friend by being there for the needy friend, by listening to the ranting friend, by forgiving the betraying friend. Which is true, to a point. The trouble arises when those friends aren't there for us, don't listen to us, and betray us time and again.
The first step is recognizing your toxic friendship for what it is: a one-way street that benefits him or her more than it benefits you. After that, you have some options:
Remember that your friend (with whom you may have a long history) is more than likely not a bad person.
She's just a very unhappy person, possibly a very insecure person, who feels she has to bring others down to bring herself up. Continuing to allow her to use you is not doing her any favors. In fact, ignoring or enabling her bad behavior could actually be preventing her from growing up and finding her own true happiness. At this level, the relationship is bad for both of you.
Tell it to him straight.
Next time he speaks negatively about a friend of yours, say, "You know, I like Susan, and I'd appreciate it if you didn't talk about her like that when I'm around." If he downplays your problems and tries to put the focus back on himself, say, "I really need someone to talk to right now. If you can't be that person, please leave so I can find someone who is willing to listen."
Standing up for yourself this way can be very difficult, but it will achieve one of two things: your toxic friend will either realize he's not behaving the way a friend should behave and start to work at being better, or he'll get mad and exhibit even more toxic behavior designed to make you feel guilty. Either way, you've learned something important: either your friendship is salvageable, or it has to end immediately.
If you don't feel good when you're around her, she doesn't belong in your life. Life is too short to waste time with people who drag us down. You could try simply letting the friendship peter out by not making any more plans with this person, but if that doesn't work (maybe you work together or both have kids in the same class) it's best to be direct: "I don't like the way I feel when I'm around you. I've enjoyed your friendship, but it has run its course and I don't want to spend time together anymore."
Losing a friend is always difficult; after all, you were friends for a reason before this toxicity started to boil over. Remember, at the end of the day, your own happiness is the most important. If you're truly worried about your friend and believe his unhappiness goes even deeper than the negative behavior he directed at you, you might refer him to a therapist or talk with his other friends or family about your concern.
Have you ever found yourself in the middle of a toxic friendship? How did you get out?