She's not evil... the thing is, she can feel lonely too.
She confessed that she feels horrible for leading you on... so just like you're lonely, she's lonely too, right? You're both doing the same thing to one another.
Don't completely blame her. As soon as she said "friend sex" right from the gecko, there was a blatant red flag. She was clearly saying that she has no ties to you.
That said, don't beat yourself up if you've recognize your mistakes. As long as you recognize that you shouldn't go back, there's at least something you can take out of this ordeal. You know that you can't (and shouldn't) handle a relationship with her, when she doesn't feel as strongly for you.