
(Spoiler Warning)
To be fair, from what I recall, that only happens over 27 years later for him, it's only in the side-stories, and it seemed mostly tastefully done and not too over the top. So I really, really recommend not dropping this excellent story over that.
Honestly, I used to feel exactly this way about many stories as well in the past regarding anything remotely involving marriage or children, but, from my perspective, as you grow older, you gradually find that the importance of family in life is actually really not to be underestimated, and just living without a family forever would ultimately be very lonely - so I wouldn't wish that on Jin-Woo either. Let's not forget that, objectively speaking, Jin-Woo as a character was always the kind of person who valued family very much since the beginning, so I think it does make sense that he would want to have a family of his own, *eventually* (like I said, it's not like it happens very soon either, I believe he was factually over 50 years old by then!).
What I'm trying to say is - let's not begrudge him his happiness and actually getting to lead a somewhat (certainly not quite! :D) normal life with his loved ones after all that time, because, considering his personality, I don't think Jin-Woo could actually be happy just living all alone as the immortal Shadow Monarch for all time - so I think objectively speaking, it's a good thing for him that he would have a son who is like himself to be by his side.
To be entirely honest, I'm not that big of a fan of Cha either - she comes off as a little bit too bland to me at times (though that may just be my jealousy speaking ╮( ̄▽ ̄)╭). But I feel like Jin-Woo deserves to be happy too, aside from just being cool all the time and saving the world, you know? ;)
(Plus, you have to remember it would only make up a single human lifetime for Jin-Woo either way - and that's like the blink of an eye to an immortal god. We don't know what other interesting things he may still get up to many centuries later (^ᴗ~) )
Just found out there’s gonna be romance in this manga... I’m so mad, why ? . Im gonna have to drop it, FUCK!! ╥﹏╥