Arnav is still affected by Lavanya, so he can't help but say yes to the offer of going out. He is affected by Khushi too, but its too early to be significant. Lavanya just breezes in and out of his life so easily. Leave him when it suits her, walk right back when that suits her too. If Aman and Lavanya are so nice and helpful to people, where did that go in case of Khushi? Why did she get the worst treatment? Its good Arnav is noticing their reaction to Khushi.