Hey @GlassHeart,
First off: it’s wonderful to care about other’s well-being. It’s part of what makes this world a better place and it’s a very natural feeling. You have a beautiful sense of awareness and capacity of empathy. So, for all the people you gave your energy, time, attention and support: thank you. You’re awesome.
Secondly, congratulations on being aware that you can’t help everyone and you also need to take care of yourself. It’s awesome to be willing to help others. But it’s also so important to set healthy boundaries, to say “no” when it’s needed, to practice self-care and work on yourself too.
Helping others is well-perceived, it’s valued, but sometimes it can be unhealthy too - because we’d be driven by wrong motivations, because our expectations would be too high, because we’d stop being aware of how we feel or even because our emotions are actually all over the place. There could be many reasons. And it’s not easy to admit this. Yet, that’s just what you did. So again: congratulations. It’s a very, very positive awareness that you have here.
I tend to be annoying with people who are close to me with this, but I really defend the idea that 1/ helping someone is not only about the other person but also about ourselves; 2/ it’s absolutely okay and healthy to acknowledge that. It’s a personal perspective - can totally disagree with this, it’s okay. I just believe that there is this general almost romantic idea that being supportive for someone means sacrificing a part of yourself, but I truly believe that this is wrong. Because we all have a background, a story, personal references and inspirations that drive us to do what we do. Being aware of our own journey and boundaries is part of creating a safety net for the people around you and for yourself. It’s actually a way to help others. Being supportive should never be at your own expense. Just because it can be very damaging for everyone in the long run. So again, it’s truly positive to be aware of why you feel this need to keep telling to everyone that you’re ready to help.
I keep telling everyone who seems sad to talk to me or hmu whenever they feel like hurting themselves or feel horrible in general. It’s becoming overwhelming and I feel like … I don’t know! I feel like I’m being selfish because I could be saving a life, but I’m too scared or too anxious because I don’t know what to say and I could say the wrong thing and I could firk it all up because I’m hopeless.
You have a precious gift: a deep capacity of empathy. But it can feel like a curse sometimes. Because life happens and we don’t necessarily have all the energy and commitment that we want to have when it’s about caring for someone.
I really want to really push away this thought that you have here: it is never selfish to set boundaries and take care of yourself. Being honest to yourself and others is a way to be respectful to your needs and others needs. Saying “hey, right now I’m not able to help you, I really want but I can’t” is absolutely healthy. And if someone doesn’t understand or respect that, it’s not your fault. For sure, there are ways to say it, and it always depends on the relationship you have with the person you’re talking to. But as for a lot of things, communication takes practice. And it’s okay to say “no” to someone.
I hope what I’m about to say will not sound rude (just because written messages can convey different tones - just so you know, there’s nothing aggresive in what I’m saying 
): you can’t save people. You can’t “fix” people, and people are not meant to be fixed. But you can encourage them. Support them. Listen. Provide resources, insights, experiences, thoughts. And yes we can all need, at some point in our life, build a supportive system around us because life can be really really hard and painful. But I believe that ultimately everyone has already the skills and strengths they need in themselves. Someone who cares is a helper, not a savior. And I think that when you learn to distinguish these two roles, then you allow yourself to set healthy boundaries (and to have healthier relationships with people around you). You allow yourself to acknowledge the person next to you, but also yourself at the same time. You have a life to live, and you live it for yourself first and foremost. Nothing selfish in this, it’s just a fact. And through this life, there are ways to give yourself and others enough space to communicate and do life together in a way that remains healthy for everyone. 
music fills the void. talking fills the void. writing fills the void.
but the second I’m alone
it all falls APART!
Well, that sounds to be a good thing to start with: learning at your own pace to handle this loneliness - whether it’s when you are physically alone or with others. You mention music, talking and writing. These could be some very positive tools to learn to know yourself, to acknowledge your needs and to communicate with others in differents ways than through supporting them.
How you feel is okay. And it sounds that you didn’t allow yourself to actually face those feelings. I guess we’re all prone to do that sometimes… trying to focus on something different, being busy and running away from our emotions. It’s a very human reaction. I’ve been there many times, especially with work. And through the years, practicing mindfulness, little by little, happened to be very helpful. At least to learn to acknowledge and identify how I feel, without any judgment, and to allow myself to be. As for journaling, this could be an interesting way to reconnect to yourself.
Sending hugs to you. I hope you’ll allow yourself to rest today. Take some time for yourself. You have 100% the right to do so.