How do i get her back?

There's a girl , my ex and now were best friends . Shes with my mate and im still crazily in love with her. Me and him are opposites im the flirty outgoing type hes shy and quiet. She doesn't like this, shes told me , shes even asked me to talk to him about it. Most of all i want her to be happy but i hate seeing them together. What can i do to : A get her back or B get over her. Thanks