I don't think they are both bad in the beginning so much as not on the same page. Leo isn't an attentive partner and instead of saying something, JK stewed in it. The latter expects an apology from his boyfriend of five years whim he knows doesn't understand what he did wrong on his side. One needs to be less self-centered and the other needs to communicate better. Very human.
But the f-buddies was a left-field moment that didn't deserve that level of mistreatment. That's where JJ went bad. Before, no one was. Now, he's currently the one in the negative with Leo in neutral wondering what he should do but going with the flow for now.
Team Leo forever idgafffffff ts pissing me off