It's definitely just a high school fear (mainly for girls)
People don't really care when you get older, such as at university
We all have different schedules, so it's common and not "uncool" to be eating alone
Personally I love it - even in high school sometimes I'd just wander off
There's no need to be so dependent on people; sometimes it is nice to just be alone for a little while.
However, the notion of sitting alone in classes/lectures is interesting even at university
A lot of girls, even guys sometimes hate sitting alone in lectures
Again, as an independent, I only really have one serious friend on my course so it isn't uncommon for me to be sat alone
And again, I don't care