Hi Robby,
Here are a couple of books focusing on a partner's perspective that I found spot-on. However, please be advised that your SO's reaction to reading them is still highly unpredictable.
Erhardt, Virginia. Head over heels : wives who stay with cross-dressers and transsexuals
Vitale PhD, Anne. The Gendered Self: Further commentary on the transsexual phenomenon
Maynard, D. M.. The Reflective Workbook for Partners of Transgender People: Your Transition as Your Partner Transitions
Green, Jo. The Trans Partner Handbook: A Guide for When Your Partner Transitions