Indeed, caring for someone else can be absolutely draining when we have so little to give ourselves. I had to tell someone else recently that I can't be the friend he needs since I can't even be proper support for myself, let alone another person who won't even help me help them... I felt so bad saying that, because I know what it's like to need someone, but I had to be honest with him about it. It will save us both a lot of pain in the future.

Edit: But also I do enjoy having someone to care about who I don't feel will want to die if I say the wrong thing (that's just too much pressure). I love caring about my other friend for example. He's pretty with it as far as mental health goes so he doesn't need me, but I can still feel like I'm helping if I cheer him up and toss cuddles at him.