My husband believes he is within his right to pursue his self-exploration
He totally is, frankly. As a libertarian, I often throw out the word "liberty" but I sometimes forget that not everybody connects "the freedom to make your own choices" with the natural inverse "the responsibility for your actions."
You husband IS free to do what he wants. But that might hurt you.
Now, if it IS hurting, the blunt question for you is "How close do you remain to people who hurt you?" For me, that answer is "Not close at all."
You expressed concerns and aggitations to us. Have you expressed them (and the reasons) to your husband yet? That would by my first step. He sounds like a jackass, and you seem to view his actions as "manipulation" backed by his profession. Perhaps he's not though, maybe he's just ignorant of how this is all impacting you. That's YOUR responsibility to share because you're the only one that can.
How he reacts to it will dictate his character. And that really has nothing to do with polyamory or monogamy, just good, healthy relationships.