Promise
Promise is one of the words in the English language that Harry likes to use as seldom as possible. It solidifies plans and is the perfect catalyst for ruined relationships and broken hearts, when said promise needs to be broken.
He’s never promised to return from a mission, because things could go wrong.
He could be lost forever in some underground bunker.
He could be killed.
Therefore, the promise he’d have made back at HQ would be broken. A moot point. Not worth the air he’d used to speak the word itself.
He’d wanted to use the word once upon a time, but things hadn’t gone as smoothly as Harry had hoped. He wanted to come back to HQ after his trip to Kentucky, and he’d wanted to make an honest man of himself. Perhaps convince Merlin to actually marry him. They’d been together over thirty years, but Harry was a romantic and he still liked the idea of matching, meaningful rings.