Taeju didn't have amnesia he just didn't recognize Dojin at first because he doesn't look the same as he did back then but in chapter 79 he recognizes him.
He didn't get amnesia it just happened so long ago and there was so much going on in Taejus life that he didn't even remember the younger brother until he's reminded about their first meeting later through a little info drop.
So like .... If they sort of knee one another before how come dojin didn't recognize him at the beginning of the story?
I read this like one or two years back and it was kinda at the end where they were being fluffy and cute but now that I went to read around ch 79 and afterwards it says they knew each other from earlier and taeju got amnesia or something and I'm confused can someone explain? ╥﹏╥