how to deal with grief and guilt

my friend got diagnosed with cancer (stage 3 rhabdomyosarcoma) at the end of 2022 at 15 and he passed away in march. we drifted the last few months before he died and i don’t think i’ll ever forgive myself for it. does the guilt of not being there ever get less? will i be able to think about him without it hurting this much? why is it always the kindest and people most deserving of long, peaceful lives who suffer the most and leave too soon?