If you're an actual registered therapist and get paid to listen to problems and help people better themselves, then this article doesn't really pertain to you. If you're treated like one and aren't actually one though, then this article is what you've been needing to hear:
You are not a therapist.
You should not have to act as a therapist.
You are not responsible for anyone's well-being besides your own.
Now, that's not to say you can't help your friends and loved ones with their issues, but it's important to remember yourself. Yes, sharing and comforting are important to a relationship of any kind, but there's a point when it becomes emotionally draining.
There are a variety of reasons a relationship can become emotionally draining, but there's only one thing to do when that happens: reassess.
Figure out what's going on, whether that's internally or externally with the person that's draining you. It doesn't matter who they are or what they mean to you, no relationship should be exhausting. Every relationship has its difficult times, but there's a difference between "rough patch" and "constantly draining."
A good sign is when you want distance and find yourself not wanting to close that distance.
Another sign is feeling fatigued after any interaction with them, like having a headache each time or even dreading having to converse with them.
If you need a third sign because the rule of three is a beautiful thing, you may notice that you're giving way more than they are—constantly.
You may be able to salvage the relationship because they may be unaware of what they're doing and fix themselves once it's pointed out, but most of the time... I would say it's time to end it. Take time apart. Learn to love and care for yourself while they fix themselves.
Doing this is healthy.
Doing this is necessary.
If you're worried about seeming selfish, don't be. Selfishness is perfectly fine when it comes to your own well-being. In fact, it should be encouraged. The idea that anyone should have to bend over backward for another person is absurd.
Actually, I take that back: it's bullshit.
What someone else does is on them, not you (provided you weren't causing any kind of active harm like abusing or bullying).
Love yourself. Cherish yourself. Don't let yourself become a therapist (unless that's your job, then please be a therapist).