( ・∇・)

I dont know why it's not obvious to people??
When the photo was taken, taku asked haesoo to think about how he would feel if he lost a loved one or something along those lines and haesoo thought of joowon I.e. what it would feel like to lose joowon forever.

And as they finally broke up, taku's photograph reflects how he feels right now that its amazing like looking at a mirror into himself(ah I really am sad about the breakup and many other thoughts) so that's they he cried and it probably gave him some closure (just my opinion).

I always thought taku wasn't there as a rival but someone who would finally get these two to move on or get together as I never liked taku because of his creepy infatuation to haesoo. Rival characters have this vibe takus doesnt, hes just weird because he hunted down haesoo after he saw that article haesoo wrote about loving his step brother, ew sounds like a kink.