I can't really empathize with the MC here, because he is pretty much an idiot. His problems are all the consequence of his own bad choices, which he follows up with more bad choices.
Let's start with not learning from his previous life. How dumb do you have to be to get a new start in a brand new world, filled with monsters, places to explore, and adventure, and fall into the same life you had in your old world? He had an excellent relationship with the female warrior, she liked him back, but he still married the princess he didn't know anything about for no reason. A marriage that also forced him to give up the excitement he enjoyed and set him up to be exploited doing paperwork. Because aparently, after defeating the demon lord, he still needed to "prove" himself to the king. All so he could then be king, which he also clearly doesn't care about.
If he had given his own path any thought, and made the choices he wanted, he would not have ended up (again) in a loveless marriage with a job he hates. But he let other people, people who owed him their lives mind you, push him into a position he hated because like any japanese MC, he can't say no.