I do think you are providing the "family guy" need for your W as you suspect. Much as I do for my W . You have also been the one certain person in her life. despite everything you have not turned your back on her. OM has finaly shown his true colours and she will lean on you for support I guess. You obviously have 2 choices now , one to provide that support and be her friend. How this will work out who knows? Possibly could be used until she finds a new OM ? The other is to pull the rug out and offer no support , that may force her to make the tough decisions she needs to make if she realy wants you to be part of her life. I think you have done enough ground work for her to really miss that . I think like me that is not in your nature .
Good luck , I feel things are only just starting to get interesting for you.