I'm not interested in 'random' sex. That implies I don't know the girl first, which is totally against my style. I'd at least like to know a little about the girl I'm making love to. ;)
Friend has the same problem. Whenever her room mates are out she gets depressed. Maybe it's just a part of their personalities. I tend to see everyone as being more extroverted than I am. I'd probably handle living alone very well since I do it all the time.