What should a girl do who has fallen in love with a young man online, fears her family and his family rejecting their marriage, especially after a previous bad experience, and feels remorse?

Love and establishing a relationship between a man and a woman who are not mahram (definition) is unlawful (haram (definition)) in Islamic law. All contact with the boy must be severed, as sins lead to one another. Furthermore, means of communication that could lead to such a relationship, like chatting and other similar platforms, must be abandoned as a pre-emptive measure against the forbidden. One should fear Allah with regard to hearing and sight, and ask Him, the Almighty, to grant a righteous spouse. For whoever fears Allah, He will make for him a way out and provide for him from where he does not expect.