OK
Ask her name, talk to her, ask about her job, and what else she likes to do.........see where it leads.
If she confronts you about checking out her behind, tell her you thought it was very attractive, and fits her well.
She if she's single, if so, see if she wants to spend some more time...
Delete him as a friend ASAP
You don't really want to find out what his problem is, or have anything to do with him..........he sounds sleezy/scary/manipulative.
Save a copy of what he send to you, in case of any questions later.
Sorry
Luck
It's done, you can't undo it, who is your ex...
Sounds like a bad fit.........from your explanation, you were attracted simply for the sex, now she's not interested.
Doesn't sound to me like she's using you, sounds more like she got hurt, (no girl wants to be known as "easy", that's the rep she's got, and part of what attracted you to her)...