The Jealousy Workbook by Kathy Labriola
You mentioned her breakup book, but I absolutely recommend Kathy's Jealousy Workbook for folx who are new to poly, especially those opening up an established, heretofore monogamous relationship.
It is possible to have a triad that's not just in the bedroom. But it is challenging to maintain. Couple's privilege is a huge issue. I've done triads and quads in the past, and wouldn't mind doing it again. But it is definetly harder than monogamy and dating separately.
This book might be useful to you, also. The Jealousy Workbook: Exercises and Insights for Managing Open Relationships.
The Jealousy Workbook: Exercises and Insights for Managing Open Relationships
by Kathy Labriola https://www.amazon.com/dp/B00FJGNVG0/ref=cm_sw_r_apan_Z4F55H8K3K2JW6NTXQ0J