I would have responded to her fb message with something like...
'I'm sure we could have put our heads together and come up with something, but you have a boyfriend now. Give me a shout when you're not 'tied down'.
This response does a few things.
#1, it poses a challenge to her.
#2, it shows you are not desperate or need her attention.
#3, you demonstrate your independence.
Me: U like texting me at random hours of the night huh?
lol
Her reply was a simple: I do that a lot, yes...
Look at these 2 messages. Which one comes across as playful and attention seeking, and which one sounds independent and in control? You're not going to get anywhere like that. YOU have to control the dynamic and interaction. You are not going to do that with a bunch of smiley faces and LOLs. I know it sounds trivial but it makes a difference. Your text messages should be brief, vague and to the point. Food for thought...
At this point, I wouldn't even respond to her. I would wait it out and let her initiate the interaction again. If she doesn't, who cares...she's got a boyfriend anyway. You are probably saving yourself wasted energy and/or drama.
If she does contact you again, try to control the dynamic. Throw the boyfriend thing in her face with comments like 'hey, don't text me to much, i don't want you to get in trouble'. Girls get so twisted with these types of comments because they're sooooo 'independent' *rolls eyes*. Don't be surprised if she responds with something like 'whatever, i can do what I want'. THAT is the Green Light to toy with her.
