Their relationship will be unhealthy if it were that of love. But theirs are more like partners, and they both know it.
Marriage can also be used when you two have the power that each other is lacking for that one goal you share, and that is their case. It isn't uncommon, especially in the past, right?
Though Dowun has a bigger influence than she is to him (for now lol), I don't think it's love just yet. It's more of "this person is important to me. He's the first person to talk to me, teach me, helped me, and to be called 'my'". It could bud if they both work for it though.