This is always my thought about a pair of immortal x mortal though... they maybe have a happy ending... but that isn't forever, sadly.
Honestly "immortal x mortal" is my fave ship trope of all times or the "all too powerful being x sickly person who's about to die in the next few episodes" bc I love SUFFERING (´°ω°｀)
Hahahahhaha, try reading Royal Servant, that's is the only Webtoon I can remember for now... also Tales of yellow dragon...
The tale of the yellow dragon is definitely on my list, however I had to drop royal servant as rape, abuse, traumas, and toxic relationships oftentimes repulses me. You may or may not be familiar but in akatsuki no Yona, Zeno x Kaya is the perfect embodiment of that ship
or Maquia and Ariel from sayonara no asa ni yakusoku no hana(though I don't ship this one romantically) ( ･﹏･)
After reading this all I could think of was what's going to happen when the human dies and the goblin continues to live on alone and depressed. Also if he ever finds someone to love in the future because if he's immortal then it's just an endless cycle of pain. (￣∇￣")