I personally think that love, mutual understanding and trust goes hand in hand. So If you really love someone you must know that person at least 95%. So If Arnav really love Khushi, he should, after the first shock and anger of seeing Shyam and Khushi's on the terrace, start to gather his thoughts and think cool headedly if the Khushi he knows could without any reason tell Shyam to leave his beloved sister.