I don't know what to tell you. You are in a very difficult situation. If you really can't avoid being around her, at least keep your contact and conversations with her to a minimum (like on a business level). No exhanging 196 text messages. I don't even exchange that many text messages with my BF. And I suggest you speak with her also to try her best not to approach you unless it is work related since she already knows how you feel towards her. She needs to help you get over her and not encourage you to have this deep seated feeling that just won't go away.
This needs a lot of effort and self control on your part but Brandi needs to help also by distancing herself from you. It's just not fair to both of your kids and spouses.