Is it considered an injustice for a young man to exploit an innocent, naive girl to establish a relationship with her and then abandon her, using a highly alluring approach to attract girls, while the girl suffers from heartbreak and regret and he feels nothing?

If the young man did not coerce the girl into illicit relations, then he did not wrong her in the common sense, rather she was the one who responded to his invitation to sin. Nevertheless, the young man is not absolved of sin and wrongdoing because he led others astray and invited them to the path of Satan, and he bears the burden of whoever followed him in his error. Therefore, the questioner must repent to Allah, be wary of the schemes of human and jinn devils, and warn other girls about this young man if she knows that he intends to lead them into sin, while concealing herself and not exposing what transpired between them.