I think the longest time I was ever single was like 16 years. Then I had one "good" relationship, I guess you would call it. Then I had a SLEW of absolutely terrible ones. *Shudders* I don't know what I was thinking. My definition of single is when you do not consider yourself to be in a serious relationship. To explain further, you can be 'dating' people, like going on different dates with different people to test the waters. That's being single. When you pick a person out of the bunch, I think you're still single. Then you start growing together, sharing things, developing a bond. At some point in there, I think you go to being, 'unavailable'.
However my past boyfriends had a different definition. They told the person they were dating that they were unavailable, while the entire state was told they were open for business. Floozies! Every single one of them!
Ugh.