i really think karthik and nandini make a nice couple BUT there is a but, she needs to change herself for it.
this is what i think should happen:
nandu should regret every single thing she did to hurt suman. then go apologise to her, actually meaning it. then she should go to karthik and ask for his forgiveness but he shouldnt forgive her easily. to prove that she means it she should say to him that from now on she won't touch him or go near him and will sleep on the floor, and will wait till he accepts her. this is when karan should re-enter, suman accepts him but it takes her time to get him back into her heart. even though karthik won't be able to love nandu the way he loved suman he can accept her slowly and give her some space in his heart.
i think it will work this way for both the couples. do comment đ