Did the young man wrong the girl by abandoning her after promising marriage, and is the impossibility of their union due to differences in countries and customs a reality, and why did he abandon her despite loving her and not finding the qualities he desired in his future wife?

You have wronged yourself by opening the door to communication with this young man online about love, thus falling prey to him. He deceived you by saying that love is not forbidden, while what is meant is this type of love based on conversations, which is indeed forbidden. It is not permissible to judge a young man as a suitable husband merely based on online conversations, as many marriages founded on this type of acquaintance often fail. Our advice to you is to repent to Allah and praise Him for turning this young man away from you. Ask Allah to grant you a righteous husband through lawful means, while being careful to seek consultation and perform Istikhara.