I think the writers are slowly pointing out certain things and are giving us major hints. These hints are so poignant that i could not ignore it.
Riddhima asked Vansh if he had any Best friend and Vansh just went away. Kabir and Vansh might had a solid friendship in their college or school years and then this friendship eventually has turned into enmity.
Kabir burn all his pictures with Riddhima.which is indicating that now Riddhima will never b a part of his life. The way he burnt it,i felt bad for the girl. Ishq mein never fail to surprise us. Msy b he wants her to b Vansh "s play thing. May b they are still best of friends and using Riddhima is just a toy for them and eventually they will turn to true enemy when Vansh will fall for Riddhima. Idont know the third possibility that I mentioned is quite weired but Kuch vi ho sakta hai.