Not all history has to be romantic.. artists only need to look at each other and every idiot jumps the Ship conclusions.. whereas say in 1000 or so active idols in 20 years, barely a handful have had any romantic connections.
Statistically insignificant.
Far more relevant is the working connections via producers, session musicians, lyricists/songwriters etc. - that is the network that actually results in collaborative work. Romance is just an occasional by-product.
"Bad boy" is yet another of Kpop's exaggerations. Groups barely 5-6 years old are discussed in terms of "eras", even regularly releasing groups are termed as "comebacks" - meh...