I think your categories are screwed.
I'm in a string of relationships, and just got out of a not serious relationship only to head into another not-serious relationship. Since you defined 'serious relationship' as being having a 'girlfriend' and single as being without, then I suppose i am in the former category . . . but I hardly consider it serious. perhaps you should redefine your categories to the following:
1. In a serious relationship - I think everyone knows this means marriage or considering it.
2. In a fling - which is where i fit in
3. I have no prospects except my hand
just my take on the matter.
