What is the punishment for someone who exploits a girl's desire to marry her in order to commit illicit transgressions with her, and then leaves her?

Deceiving and defrauding women to violate their honor is a forbidden act and a disgraceful conduct, amounting to zina (fornication/adultery), which is one of the greatest major sins that incurs Allah's wrath. The greatest danger lies in belittling the sin and having little shame before Allah, for the lesson is not in the smallness of the transgression, but in the Greatness of the One Whom you disobeyed. The perpetrator of such an act must immediately repent by abandoning the sin, regretting it, and resolving never to return to it, while concealing it and not openly proclaiming it, for whoever has committed any of these impurities should conceal himself with Allah's concealment.