WHAT IS THIS SHOTA SOMETHING LOLI THINFS LOL WHAHAHAH BUT IS IT PINK X BLACK HAIR
The Baby That Master Brought is Sus!
https://www.mangago.me/read-manga/the_baby_that_master_brought_is_sus/
its not this one its not a webtoon and the boy returns back to normal! It also starts out with an established relationship! not pink x black hair either!
while this manhwa isn't the one you're talking about it is quite exactly what you described lol.
It's a yaoi or shonen ai where basically the boyfriend turns into a child out of nowhere overnight. a Please help me find it!