It's ComicDom (a.k.a. the notoriously scummy group formerly known as ComicPlus). Expect translations to often be pretty decent, but have some really weird inconsistencies lol
..so he married her into another country's Royal House..
I'd say he wanted to take over in a clean manner (leaving her in the country after his ascension would still have meant a split loyalty and she would have been an annoyance at best or a risk at worst).
But it's also clear that beyond pragmatic politics he also wants her to have a good retirement deal, so tossing her out (no strings attached) is pretty much the best he can give. So there is love there, but perhaps not as selfless as you might believe.