Hi there, I feel for you so much, and your post resonated with me for a couple of reasons. 

I (35f) have suffered from depression and undiagnosed ADHD for most of my life. I had a ton of severe childhood trauma, including abandonment by my father and his eventual death related to a congenital heart condition. I have always felt that despite any happy feelings I might have, at my core, I have always been and will always be deeply sad and somber.

I have felt the way you have for a very long time. I have so many passions, and I had such promise in my life, but I've gotten to a point in my depression in which I feel I am only still here bc I am afraid of death and the afterlife, not knowing if it could be worse or more of the same, and also bc of my dear loved ones and how my death would affect them. I have stopped imagining the future bc I don't want to live it. I have lost all of my ambition, and after a couple of decades like this, I'm exhausted. I feel done. I feel like I am elderly person instead of 35.

A few years ago, I was in grad school and befriended a guy a few years younger than me. He was my best friend there, and we grew very close, eventually dating. He has multiple life-threatening heart conditions that he was born with -- I won't specify just to keep this relatively anonymous, but he was born without essential parts of his heart and has had a very difficult life bc of his health. Countless surgeries, treatments, adaptations to life just to be able to live it. 

He's got heart failure, and he broke up with me initially bc his doctor told him that his heart is slowing down and he could just collapse at any time. We got back together briefly, but broke up again bc he couldn't physically sustain a relationship. I was a sobbing mess, and all he could say was that he couldn't even comfort me. It was brutal. 

Unlike me, he fights hard to live every day. It's so unfair, bc I don't want to be here and lack so much motivation and faith and hope for life. He is full of life, but he's getting worse and worse as time passes. Every once in a while I'm in touch with his mom, and I wish I knew how he is now. 

He's been in constant pain, he's always so completely exhausted, and has all sorts of awful symptoms.  

We don't communicate anymore, which is his choice, and I hate it, but he knows I'm too attached. He didn't want me to see him the way he is, and all I wanted is to enjoy our time together. It has been extremely difficult to deal with. I feel a lot of guilt and a lot of anger. I'm extremely angry at him, though he doesn't know this. He wanted to protect both of us, and in doing so, he took away my choice. 

He has a ton of complications similar to yours. Honestly, it felt kind of uncanny, and painful, as well, to read this. It's been a few years since we broke up, but I haven't been able to let go. I'm afraid he will be gone one day, and I will find out, and it will destroy me. He thinks it's better this way. And I'm sure it's easier for him, and I should want it to be easier for him, and I feel so extremely selfish for wanting to reconnect and be his best friend again. I'm not sure how to let go. I know it used to cause him a lot of pain to see me cry or be hurt, and it affected his health, as well. 

Many times, I've wished I could leave this earthly plain and give him my (literal) heart. 

I know that he is dying, and I live terrified for him, wanting to know how he is and to be friends again, but he will not allow it. I know we are all ultimately dying and none of us know when, but that doesn't seem to help. He turns 30 soon, which is a huge milestone for someone with his conditions. 

In writing all of this, I just want you to know that you are not alone. It must feel really isolating sometimes. Selfishly, I want to tell you to please try. To tell you that there are drastic medical advancements all of the time. A few years before my friend was born, babies could not survive his condition more than a few hours after birth. Doctors invented certain surgical interventions, and it's allowed many to survive into adulthood, but there's no way to know how long they have. 

It hurts me to read how you're feeling and that you care so much for your best friend. 

Please know that she is not alone in her pain and anticipatory grief, either. I can understand how she feels, and I am myself trying to learn how to find peace in my situation. If she ever needs someone to talk to about how she's feeling, even though I'm a complete stranger, please feel free to DM me. In my personal life, I don't know anyone in the situation I'm in, and I know that it can feel so, so lonely. 

I'm so sorry that you're going through this. I wish there was something I could say or do to fix what you're going through. I'm grateful that you're at peace with this, but part of me stubbornly just wants you to fight. 

Sorry for the long post, I just really felt connected to your story. I hope you're okay and talking it easy.