She's a monkey swing in the trees. She won't let completely go of the last branch (you) because she's not completely sure of the stability of the new branch (OM). Why? Because he's a nasty cheater. She knows she can never trust him and he can't trust her. That R is doomed from the start so she feels if she keeps you dangling as a plan B that makes her feel more secure in her new R with douche bag.
You need to remove yourself as an option. People want what they can't have. She toys with you because she knows she can have you anytime. Admit it. If she called today and said I want you back, come pick me up, you'd drive over there so fast you'd get multiple speeding tickets. She knows this and that's why she treats you this way.
