Why is Jessica sad to see Lancelet go?

THis is actually in Act 2 sc. 3

Jessica, the daughter of Shylock, meets with Lancelot and tells him that she will miss him after he leaves to go work for Bassanio. She enjoyed Lancelot's humour and considered him a confidant.

Because he was the main "light" in her life. She was depressed because she had to live with her father whom she did not connect with. Lancelet however, was the only person Jessica loved. He made her laugh and happy.