i have the feelings that natasha might have called aman for help. i remember she said that she will get engage to arjun in one month..so to fulfill what she said, she wanted someone to help h er out and she knew aman would be the one to separate arjuhi..she know salil is useless (as we have seen he has nothing else to do than going to purbi's house and meeting her wherever possible) and her other brother is too busy with his gfs.