Is it sane to have a first date with someone new and declare you are in a relationship?

[Zardoz]

Follow up on my last question. This girl I was seeing (for a year until last Saturday) went out with a guy for the first time on the 7 March 2014. She changed her Facebook status to 'In a Relationship.'

What makes this worse on the 8th, she told me she wanted to be friends and enjoy the single life. I am completely confused.
She is 33, so it makes even less sense.

[Eliot K]

If she is younger than 25, then there is nothing surprising about what she is doing.

[bin there dun that]

Geez Zardoz! This must have surprised and hurt you. I think in the long run you are better off without someone like this - she can't be a very sensitive or caring person to post that kind of information to FB without speaking with you first.
Is it sane? Sounds more like infatuation.
You can do better than this. Take care.