Why did you go radio slient?

This is my bud/brother of 15 years has gone radio slient on me. He’s gone slient before a few times. Longest being 1.5 years. This latest slience is 5/6 months. No replies to texts. I called today but staight to voicemail. I get we handle life differently. He’s avoidant to sharing feelings. I don’t push hard but let him know I’m here and I care. But this latest round of slience feels damaging to our friendship/connection. We didn’t have a fight. Nothing. I feel he’s dealing with a full plate in life. But to shut me out this long? Everytime… I feel/think.. dude, atleast lemme me your okay and need time/space. I feel like I am an annoying ex gf by reaching out. I dont think im over doing it, I check in once every few weeks. But I’m gonna stop reaching out and see what happens. We’re both 35. We’re grown guys. I find it confusing, I’ve express my concern. BUT I’ve gone slient before myself but only for a short time. But not months and months. Not forsaking my buds. Idk man. So, just trying to understand radio slience, how long did you do it and why?