re: what are some circumstances that have ruined long term friendships?

People mature at different paces or simply interests change over time and slowly lose track. As people get older they're less willing to put up with people's shite. Something I may have put up with at a younger age to have friends or someone to hang out with, I just don't anymore. Most things I'd rather just do alone.

I've lost a few close friends to marriage and/or kids. Still considered friends, but just live different lifestyles now and find different things entertaining.

Also, relocation for jobs, etc.