Watch the older brother be in love with the younger brother and only hit on other dude because younger brother was interested in him.
Other dude and younger brother get together in the end and older brother pouts, throws a tantrum, and tries to get in the way the whole time with younger brother excusing his behaviour the whole time.
The end.
Of course, this is just a guess. Hopefully it proves me wrong.
With every passing chapter, all I could think of was "just break up with him already" - sadly it took over 70 chapters for her to realize her own mistake. Despite this complaint, I enjoyed the realism of the story and how it captured not being able to let go of someone even though you know they're bad for you because you love them.