From what you stated it definitely sounds like she is interested in you.
if she always trys to make conversation with you it means that she really likes you so therefore wants to talk to you and if she smiles it means she's happy to be with you
She probably likes you. Smile back.
He goes behind your back and tells his mates he's shagged you, even though he hasn't.
If there Around you wen they can be, you notice them staring at you, and she smiles alOt when your near her
She could like you, or feel really comfortable around you.
that means he likes or because your staring at him.
He really likes you.
It sounds like he finds you attractive and is interested in him. If you like him, smile back and see where it goes from there.
A smiley face.
A Cheshire cat.