I knew this would happen when Richard and Duke Henry started messing arround. Now he wants to betray them if he can't have them as his woman? Worse still Duke is sending an oblivious ex lover to do the dirty did. My head hurts... 😖

The one who he sends is probably one of those ironic jokes the universe tosses at them everyone every once in a while.
When laugh about those too much, it will push one to the very tip of sanity.

Henry Buckingham expects 100% transparency in return for his trust but failed to see Richard's nature, of course Richard would still keep stuff to himself because that's his nature and he can't just start talking about stuff that is censored by his subconsciousness.

They fly way too close to the sun, and burn terribly.

he's basically acting like an psycho ex

Yes pretty yandere, he builds delusions even fully aware how his feelings for Richard overwrite his usual cool headed thinking.

This is probably being among the reasons Richard stays detached and distant to others, this happens if you allow them to get too close.

Then one day you fail them and their great love turns into wrath or murderous intent.