Well, I love living alone, but there are two things that always make me rethink living alone. (or at least keep me awake all night with all the lights on, watching Say Anything for the 74th time.)
1. Bugs.
2. Wind Storms.

about number 1: Last night I found a bug in my apartment, and for the first time actually had the courage to buy those bug compartment things that you are supposed to put around the house. Congratulate me. Once, I had to beg Laurie (my roommate one year ago) to leave a bar, come back home, and kill this huge water bug that I saw on our wall. To my surprise, she did just that (well, she left the bar. but then we never found the bug - thus making my state of panic, and state of hallucination). She tried comforting me with stories about how she had to kill bugs when she lived down South. I remember not really sleeping that night, and being embarrassed because we had known each other about 4 days. The bug thing always breaks in the roomies.

about number 2: I love storms. My Mom always tells me that my Dad and I used to get excited by thunder and lighting, and go out onto the balcony and watch the storm together. I remember doing this too - but it's always fun to re-hear stories from Moms. When it's raining I will usually keep the window open - so I can hear the rain. I just don't like windy storms when I am alone. There is no one there to comfort, and that of course makes the wind gusts sound like burglars, and giant sized Bugs, and killer tomatoes attacking the apartment at 2am. Keeps me stone cold wide-awake every time.