I trust you... But I don't trust her at all... But I'm not going to tell you who you can and can not be friends with... But honestly I would rather you not be friends with her... Don't you know what she wants? And the effects it has in our relationship??
She knew you were in a relationship right? & she had absolutely no respect for that... Why do you even want to be friends with her after that?
Yes, I know we can not control our hearts but there is no excuse for her doing that. She should have enough respect for you.