What would you do to get your son back, especially since you see him living in an unsuitable environment and you don't want him to be lost?

You erred in making your son choose between you and his father due to your anger, and you should not have handed him over to his father given his bad behavior. You must treat your son with gentleness and kindness at this critical age. Review yourself and your relationship with Allah, for problems in family relations are often due to sins. Try to win back your son's heart and supplicate for him abundantly. At this age, the boy has passed the age of حضانة (custody), so his remaining with you is not a matter of حضانة.