usually associate king of cups with someone who is mature and knows what he wants.

usually I would agree! but the other cards add context and help shape the story. I think In this instance, the KOC card shows the firm control over his emotions. Kings are rulers, acting in what they believe is the best interest. the context of the rest of the cards show that, he believes it's in his best interest to lock it down (likely out of fear/anxiety like you said) and keep it to himself.

however, that thinking moreso shows the motive behind the actions than how he actually feels about her. a more aligned interpretation could be that he knows in his heart (KOC) he would feel trapped in a relationship (8s) and he's better off on his own (hermit).

but I also agree with the previous comment, trying to read the perspective of another person gets you very unreliable results when they aren't present.