I know you hope that she accepts that has gone on for the last year and a half and moves towards being with you both, but have you thought of what your prepared to do if she says no, shes not interested and wants him to end it with you? will you keep seeing him behind her back?
will you be able to end it gracefully with him because that is what she needs? will you stop seeing each other while she rebuilds her relationship with him and learns to trust him again before opening up to poly?
what if she ends it with him and askes him to leave? what plan have you come up with to that end?
this isnt going to easy but I wish you luck.