I have one single friend and it's really eating me alive

hi! I'm a teen and have been chronically ill for a long time + homeschooled and I have only one single actual friend who I consider my closest, but we've been talking less since she's busy, and I realized how much I rely on her and just want to talk to her but it feels like she's maybe losing interest in me or that I'm annoying (I'm 100% overthinking it because she said I'm the only person she trusts, and we really are close, but she has other friends at least, and nothing has really changed between us I'm just honestly going INSANE imagining scenarios in my head obsessing over her, but still) and it feels terrible that my mood basically revolves around our fun chats that I overanalyze and convince myself that she's sick and tired of me or something.

and idk what to do, my life has fallen apart in the last year (my grandfather who I can't see bc he lives in another country might pass away soon) and every day is a struggle just to live and not have meltdowns and I don't have any irl support so it's really tough, I just don't know how to make it through day by day. i want to make more online friends but basic socialization is so tough and yeah. sorry for the vent