Sick fiancé and I’m a shitty person

So my man has been having problems on and off for 3 months. Twice we thought he’s having a heart attack but at the ER they said it’s just anxiety. We haven’t slept in weeks for more that 2 hours per night, he’s constantly in pain…Yesterday he got a heart ultrasound and it turns out his heart is leaking. They said when it gets worse the only thing that could save him is open heart surgery but only if we catch the leak progressing, otherwise it’s a heart attack and death. I know I should be telling him everything will be okay but I’ve been saying it for 3 months and nothing turned out okay! And for god’s sake we’re 24&27 years old. We should be worrying about starting a family, getting married, not about losing the one person I would literally give my life for. And I feel so fucking selfish for feeling like this when he’s the one going through it, but in the end if god forbids the worst happens he just drifts away and I’m stuck here without him. Without the man i spent 9 years with. In 9 years we haven’t spent one single night apart and now i feel so alone, even while he’s still here. And I can’t help him feel calm because I can’t even help myself. And i hate myself for it but i hate him more for doing this to me even though i know it’s not his fault. Im just so god damn mad and I was so rude to him but it’s so much easier to pull away than let the reality sink in. I want to be there for him but my selfish ass doesn’t want this kind of life. Don’t get me wrong, I would never in a million years leave his side, but I’m so scared of having to say goodbye too soon.