I absolutely hated the ending of Hyde, Jekyll, Me. The only reason the main girls gets with Jekyll in the end is because some of Hyde's personality imprints onto him. I felt really bad for Jekyll.
Kill me Heal Me has a similar premise, the main girl falls for one of the main guy's other personalities. Does she genuinely fall for the main guy's main personality in the end or is it like Hyde, Jekyll, Me?
With kill me, Heal me his multiple personality disorder is based on his a past trauma i think he had 5 personalities apart from the main one and each one was formerly a part of himself but magnified into one separate person. they're all a result of some major insecurity he deals with. I don't want to spoil too much but she basically falls in love with all the characters because they're each a major part of who he is.
It's better than HJI. Trust me. She really falls for the real personality. 
@Cactus28 - I'm good with spoilers. Would rather know so I don't waste my time on an ending I don't like.

@Soju - Good to know because Hyde, Jekyll, Me was pretty good, but then the last few episodes were just awful. Hyde overstayed his welcome.
i dropped KMHM after the first episode.  I didn't like the way they treated mental illness like a side show.  I'm one of the few who liked HJM.  it was much more sensitive.
I hated the end of HJM too. It made no sense that the writers had her fall for the "fake" person and then the real one was like a consolation prize In KMHM she falls for the real personality and she becomes fond of the others. She acknowledges that they are "separate" but all still parts of him.
KMHM is nothing like HJM... Maybe the end is scientifically worse but the romance story is definitely better. She knows he has multiple personalities before falling for him, and for the others too :) She likes him with or without the other personalities. 
KMHM is a great drama I really recommend it, she falls for the person and in fact she helps him cure his multiple personalities disorder.
/Vague spoilers since you said you're ok with it-->/ KHMH had a good ending. The girl didn't fall in love with other personalities, but acknowledged them and she was treating them like a different aspects of the main guy, trying to make peace between them and consider their viewpoints. His personality gets reassembled in the end. The triangle between two main personalities and a girl gets resolved and everyone has a closure.
HJM tried too hard to be different than KHMH, which was far more popular when they both aired, so it went in a weird direction. [Bonus fun fact: one of the two good things about that drama - the girl being badass and sneaking around buildings in an acrobatic manner - was a shameless ripoff from Hotel King.]
It's funny I hated KMHM because the lead girl didn't end up with Shin Ser Gi,but instead the main boring persona... Ser Gi was like a little cinnamon roll around Ri Jin...How could you not love him:/ I loved HJM  because she ended up with his main persona Seo Jin ...Her and Robin was just too lovey dovey to me,such a turnoff-.-
@namopanik

Funny thing is I've read the webtoon and while I didn't really like the ending either, it was MUCH better than the show's ending. She actually falls for Jekyll, but it ends with her being in a weird polygamy type relationship where the personalities switch off.