Basically, he has a grudge and doesn't care who gets caught up in it so long as a single person feels pain. He is just kind of the worst person (IMO, in terms of the number of lives his actions could effect) in this series.
In a little more detail, he is an incredibly petty person willing to destroy countless families and bring war to the commonfolk of a nation over a grudge from over 20 years ago. The novel is not completely translated and the spoilers are very select, but that is the way he looks. From my loose understanding, it is Sov's mother he has a grudge against but she is obviously not around, so he wants to crush Sov and destroy Sov's nation. Ruining Navier would help make Sov unhappy (his feelings are more complicated than what the manhwa shows), and weaken his nation. Now a lot of the later spoilers I read are contradictory or vague in detail so some of what I said could be wrong but a lot of people on NovelUpdates have pretty negative opinions of every major male character (including Heinley).
He is aware that Heinley is infatuated with Navier, but he is NOT doing what he is doing to help those two marry, he doesn't really even think of the possibility until the other characters are already making their moves.