Ed here: Yep, people lie. Even people you've had sex with. You knew it was a lie and it kept rolling in your head and you had to go out looking and you found more than you bargained for. That sucks too. And now you can't get them out of your head. Well, you've got attachment, a smidge of obsession and the fact you cannot understand why they lied or what a fool you were.
Give it time, stop looking at their facebook page and no more cyberstalking. I mean that in a nice way