Well, first speak to willingness.
Have you asked him if he sure it is about "wanting a polyship configuration shape to his romances" that he resonates with? Or he is "not willing to go steady with you and too shy to say it clearly and straight up?" that is the thing at hand. Get the clarify.
How about YOUR willingness? Are you wanting a polyship configuration shape to YOUR romances? Or do you just like taking on your romances one at a time like a monoship? Are you willing to say "No, I am not willing to participate" in a clear and straight up way if you are not actually willing? Are you willing to say "Yes, but only like this..." if you are willing because you are clear about what open models
appeal to you and what does not?
Where IS your willingness laying here on this?
Before rushing off to find someone ELSE to date and add to your configuration, how about spending some time learning together and discerning if this is indeed where you both want to steer this relationship toward? Are you realistic about potential pitfalls?
Is it in the best interest for you? For him? AND for the couple as a couple? Are you willing? Is he willing? Is the couple as a couple willing?
There's lots of links you could look at together.
Nobody ever died from going slow and steady as they assess themselves for "poly willingness" and "poly readiness."
If the couple decides as a couple that all are in full willingness and full readiness, then I hope your unfolding goes well and you both find the happiness ye seek.