I can't read Mandarin nor Korean or Spanish

However I was able to make sense of the Spanish raws via translator, and because of that I have a good grasp of Keith's character.

First off it's up to chapter 37 and I can guarantee you that pic of Keith kissing another dude was a setup. It's classic manga material used for the "make-up" scene. Just note how it's the other guy holding onto Keith and how Keith's face is a bit surprised.

Secondly, it would be a lie to say that Keith wasn't looking for Yeon. He sent out his security team to search neighborhoods as well put out a missing persons report over the news. And given the fight that broke out at the diner, I'm assuming there's a reward for finding Yeon Woo.

Third, even when Yeon was still living with Keith, and even before, Keith refused to let him go. In the next chapter of this English translation, Keith will make out with Yeon Woo (as in pushing him down on the hospital bed and feeling up his chest over and over again). For the chapters to come, you'll see Keith getting more and more possessive to the point where he tosses Yeon's pills away and has sex with him because he doesn't want to smell another person's scent on Yeon.

Thing is, they're happy together. Keith actually tries to spoil Yeon. Heck, it got to the point where they had sex in Keith's office at work.

The issue came when Yeon caught Keith kissing some chick...and Keith never apologized for it.

Yeon decided to leave. He packed his bags, wrote out the check for what he owed for breaking contract, and after Keith refused to take back the gifts and ripped up the check, Yeon tossed the gift into the trash.

I think the core of the issue is that Keith still had a rep for dating tons of women with no strings attached, even though his close friends can see that he's strongly attached and involved with Yeon Woo. He simply didn't reject the advances of others, thus cheapening what Yeon believed to be an exclusive relationship. So now Yeon is trying to get an abortion, but he couldn't go through with it.