‘NOT ONLY’ sentence without ‘but (also)’

‘NOT ONLY’ sentence without ‘but (also)’

The passage below comes from the following Utube video. The part starts at 01:52.

(55) Bellerophon: The Rise and Fall of a Tragic Hero - (Greek Mythology Explained) - YouTube

The King believed in the word of his wife was now furious to say the least. Not only had Bellerophon taken his hospitality and thrown it back in his face, but the pardon he gave him now made him a guest in his kingdom and to kill a guest in your own kingdom is to incur the wrath of Zeus. The only solution Proetus had was to send Bellerophon to his father-in-law King Iobates accompanied of a sealed letter asking him to execute Bellerophon for violating his wife.

I have two questions on this passage.

First, the 1st sentence is grammatically incomplete. It has two main verbs but no conjunction. (Am I right?) I think this sentence should have ‘who’ before ‘believed’, or have ‘and’ before ‘was’. (Am I right?)

Last and the much harder, the next sentence is incomplete in contextual sense. ‘Not only had...’ part shows the king’s reason for his fury, and that’s proper and OK with me. But the problem is that if a sentence starts with ‘not only’ it also has another information starting with ‘but (also)’, and in this sentence another reason for the king not to kill Bellerophon. There no added information about the reason of his fury, but then it just follows the reason not to kill him with ‘but the pardon...’

Do you agree with my line of thought?

If you do, could you give me better sentence in stead of the author of this video?

If you don’t, could you tell me where I am wrong?

Thanks in advance.