I don't understand him... Why he don't like siwan...

Bcz he already likes someone else..
I admit I Would've chosen Siwon over Jihan if it were me, Jihan's possesiveness is too much to handle..

Bt I understand if you already put someone in your heart no matter how better a person you meet after that, you'll always choose that very person everytime..

Actually he would be fall in love to siwan if siwan didn't left him in the moment of despair