
Spoiler...
Did They liked each other in the past? Wait sorry cause i can't read hangul but the sexual tension is fxxkin strong. And WTF i only Understand is "I love you". Did Ed say " I did Loved you?". I'm sorry i don't know but i can only read I love You in korean. Jsjdjdjeokwoejdjdjdjsjs shettttt!

It is strongly implied that Ed had feelings for Chang in the past. Chang has had feelings for Ed all along.
In the flashback, Ed comes to shower at Chang's apartment because his has no water and he doesn't want to deal with it. He comes out of the shower half dressed and is relaxing on Chang's bed when Chang notices Ed has hickies.
He asks Ed if he had sex with someone and Ed says yes and Chang asks if it was good and Ed says yes to that too. Chang asks if Ed used a condom (in a concerned way) and then makes some jokes about Ed but also snuggles him and kisses him where the hickey is. Ed let's him at first but then tells him to not because its hot.
So Chang gets off.
The scene is Chang angst because he has to accept that Ed will be with women from now on and he will never have Ed in that way.
Hope that helped.

Went back and reread to make sure but I don't think Ed says he loved Chang. He only asks Chang if Chang loved him all along and Chang says no that's disgusting and Ed is just like yeah right you loved me, your way of expressing it is disgusting, and I hope you loved me a lot because I'm going to use it to hurt you.
I paraphrased but hope that helps.
Spoiler..
I don't remember well but. That red head is investigating who is the killer is.
LMFAO you kidding right
Nope hahaha are u talking about that red head right? He is innocent