Theory

Aight, so I heard how people said how "Bum breaks into other people's houses before being with Sangwoo". BUT.

Let's do the math.
You graduate Korean High-School with 18/19.
Bum enrolled college for 4 years.
Sangwoo is 18/19, Bum is 22/23 when entering college.
Bum fell in love with Sangwoo after he saved him in the military.
Bum is currently about 26.
That means that Bum's in love with Sangwoo since 4 years.

Chapter 26 said that Bum isn't a minor in the flashback( http://www.mangago.zone/read-manga/killing_stalking/mf/c026/?av=1), so prob about 19, Jieun makes fun about Bum for enrolling college so late( http://www.mangago.zone/read-manga/killing_stalking/mf/manga/killing_stalking/c017/pg-38/)
Bum said that it's because of family circumstances.
Obviously we know why.His uncle.
In Chapter 26 again, when Bum went for a walk because of what happend in the night before, his uncle was angry and prob afraid that Bum might go to the police to report him( http://www.mangago.zone/read-manga/killing_stalking/mf/c026/15/).

That means that even though he wasn't a minor and obviously should be able to go where he wants to, he didn't had the uncle's agreement.
Bum was raped in the same night again.
Bum said to Sangwoo that he lives with his uncle( http://www.mangago.zone/read-manga/killing_stalking/mf/c005/63/), but Bum seems to be the only one who lives in his apartment( http://www.mangago.zone/read-manga/killing_stalking/mf/c001/34/).

How does he earn money for a apartment without a job?
Because of his uncle, giving him money in return to sex.

So Bum was with his uncle and(?) grandmother for 4 years until he was 22/23, moved in to a apartment, met Sangwoo in college and loves him since he saved him in the military, for 4 years.

Bum said how he "wouldn't be able to forget it as easily as before"( http://www.mangago.zone/read-manga/killing_stalking/mf/c001/37/) and asks himself why he does what he does( http://www.mangago.zone/read-manga/killing_stalking/mf/c001/11/).
He asked his own doings, like it's the first time he does it.

Sangwoo is the first person where Bum broke into someone's house.