Like something you might've heard before- the talented actresses and actors could not make up for the horrible writing of this drama. I'll admit it had me in the first quarter of the drama before going downhill. Many of the storylines were nice! And then there were more and more storylines just piling up! And then they ALL turned to shit!
Some n̶i̶c̶e̶ ? things they had going:

- The relationships between Jooin's mother, Jooin, Bisoo's mother, and bisoo. The interactions between them all were always very cute. Any scene with Haejin or Junghwa was nice to watch.
But Bisoo's mother, Haejin, was sick and eventually died with little grieving from any of the characters considering how intertwined they all were. We also see Junghwa and the other old man less and less in general.

-A love triangle. This triangle was very useless. Annoying to watch. First, we know Yujin likes Jooin, but why is that his only plot point. His whole character is about being in love with Jooin and butting in. I could get over the sweet, best friend second lead trope if we weren't randomly thrown by Jooins's 'i like both of you' in the middle of the series. Other than letting Yujin make advances on her, it is never obvious that Jooin ever liked Yujin. And then its obvious she's already made up her mind within an episode and a half. For some reason though, Yujin still acts like it is a competition until the end- which is annoying.

-Literally the name of the drama. Bisoo is suddenly Jooin's tenant. They do this little thing of having Bisoo call her 'master' which then dissolves into nothing because Jooin's resolve is weak. I'm not even going to go over the fact that Bisoo just plainly disrespects Jooin in her own house multiple times with basically no consequences. You'd also think that there would be more moments about what happens when a girl who has lived mostly by herself begins living with practically a stranger. Like what was even the point of the cohabitation aspect if it wasn't explored? Why was it even in the title?

-Jooin being a 'top star actress'. Jooin wins many awards, is on billboards and does many dramas and ad shoots. She has a crazy stalker fan that is only used in a few episodes, being soon forgotten (which is strange considering the dark scenes we saw with/because of her). She makes sure to not obviously be with Bisoo while in their neighborhood. Despite all of this- she isn't crowded with people while outside and never has actual trouble with people. Seems inconsistent.

-The public/fake Yujin relationship and then Bisoo relationship. First Jooin is in a fake relationship with Yujin. Then there are rumors about her cheating on him with Bisoo. Then Yujin refutes rumors. Then Jooin goes out publicly with Bisoo. Am I missing something? I don't recall Yujin or Jooin making breakup announcements so how come Jooin is suddenly able to publicly date Bisoo (we see them in a building holding hands while a crowd is in front of them). Nobody was going to say anything about how she either was 'cheating' on her boyfriend or about how she went from one friend to the next?

-Bisoo disappearing. Probably the silliest and dumbest plot ever. So he gets hit by a truck, is supposed to die, but is brought back with a limited amount of time because his dad wanted him to express his love? And then Jooin is talking about Bisoo. And then the drama abruptly ends. I just found the fantasy element very ridiculous and out of place for a romance like this.

-Also the birth secrets. We love some half-fleshed out birth secret storyline!
-Also the short-lived open doors trauma!

Lets not even go over ALL the plot-holes, events that should've had a bigger impact and the plain forgetting of plot points.
The cute moments are there, yes! The music is nice! Sometimes I question the stylist yea!
Not the worst but overall, WOULDN'T recommend. There are many nice love triangle, sick parent, second-chance, actress and cohabitation dramas! Watch one of those :)