I've been on both sides, and understand each. Well, some people just straight up don't care and think we're being over dramatic or something and that really upsets me. I want to be there for my friends especially when they're down, and I am when I can be and my own mental problems aren't completely drowning me to the point I can't talk to anyone. I know what it's like to need someone, but there is a limit. For instance, I had to cut ties with one friend because it was very one-sided. Our entire friendship was centered on her problems and her life. Lord forbid we ever discuss mine. She would talk over me a lot, always changed the the subject back to what she wanted to talk about (her), and she just didn't really listen to me, but expected me to listen to her. I finally got fed up and ended it. I'm sure according to her, I abandoned her in her time of need. To me, I got out of a toxic friendship with someone who didn't give a shit about me and only used me to unload on.
I do think we also need to realize the effect we have on other people, and if we cared about them, we wouldn't want to drown them in our negativity either. There does need to be a balance, and it can be difficult to navigate and I we all slip up sometimes. Not saying this is what you're doing though. I don't know your situation. It really is hard finding friends that have the strength (or empathy) to keep up with us. I isolate myself anyway when I'm at my worst, and don't naturally go to people for help so maybe it is different for me. That doesn't mean I don't still desire a friend to be there for me though, but I think deep down, I'm scared of scaring anyone away even if I'm not consciously aware that's why I do it. It feels better to think I'm the one who is isolating myself, rather than other people deciding to leave me.
I'm sorry you're struggling. Depression is a monster. I really wish it could all just turn around for you.