Believe him - he said he couldn't see you as a primary. What that probably means to him is that he wants to enjoy the time you two have together but with less entanglement than society typically prescribes to relationships. A really good book for you two to read together and discuss is Stepping Off the Relationship Escalator: Uncommon Love and Life https://www.amazon.com/dp/B01MRDI7JC/ref=cm_sw_r_cp_apa_CdyDBbXSPWCVG It may help him put into more concrete terms what types of entanglement he does and does not want.
Maybe this book will help you explore these ideas: https://www.amazon.com/Stepping-Off-Relationship-Escalator-Uncommon-ebook/dp/B01MRDI7JC
This book may help you identify what is important to you: https://www.amazon.com/Stepping-Off-Relationship-Escalator-Uncommon-ebook/dp/B01MRDI7JC
The only book that really resonates with relationship anarchy in my experience has been "Stepping Off the Relationship Escalator" - while it's not directly about RA, it talks about a lot of the same philosophies.