This is what I think
1. Shukla is DOMINATING by nature ....he doesn't like if his friends go around speaking to his enemies BUT he himself can go around fake flirting with his enemies
2. It's his way or the highway attitude that was a problem! He wants to be a leader at all times BUT in friendship one can't be a leader
Be it game plans or in general he expects his friends to follow his orders and rules and stop applying their brains ! More than friends he wants followers
3. Sana is a flipper and we all know that ! She switched to Paras and then Shukla took her in a heartbeat in an instant WHEN he himself had warned Asim against her ....this did not go down well with Asim COZ Shukla backtracked on his own words here !
4. Shukla has a HUGE EGO and that's one of the reasons why his friendship with Asim broke
5. Others like Sana , Paras, Shefali J etc. Played catalysts and put ghee in the fire
So, I feel Shukla's over dominating personality , his ego , his attitude of my way or the high way AND Asim's will to voice his opinions, to call out Shukla when he felt he was wrong PLUS other players acting as catalysts is WHAT TORE THEM APART