@practicallyuseful We don't know that. For all we know, he might have been festering a bit of affection years before he even became the vice commander, which might not have gone far, but began rapidly changing when the female lead suddenly changed herself. It starts with knowing each other, to spending quite a feasible amount of time together due to work and then curiosity when she suddenly changed, which eventually becomes attachment. Also she's pretty, so stuff keeps adding up.
As for being boring... Well, I'd give him time to develop, hopefully he'll change just as the female lead is. The thing is that just as it was put, both have near 0 social skills, so dialogues between them are difficult at the current stage since no one really leads the conversation