Hi purplefan, I think that is a reason for sure. I had depression at school and obviously other teenagers couldn't cope with that, I felt let down and I was too messed up at the time to maintain any friendships. I made one friend in sixth form but she died from MS. I was kicked out of sixth form for being too ill and not attending. I find this time in my life too painful to talk about. I kept in touch with some people from uni but lost two of those friends this year with them demonstrating some very bizarre behaviour.
I made some superficial friends from work but it always fizzled out as they had a husband and families, were too busy and any spare time they seemed to prefer hanging out with other families in the "mummy club". I'd love to reengage with past colleagues but understand their families come first.