What is the way to atone for the sins of speaking with girls, promising marriage, and engaging in forbidden acts, after repenting, committing to prayer, and memorizing the Quran?

All praise is due to Allah, who has blessed you with repentance from those sinful relationships. You are not obligated to do anything towards those girls. However, you must remain steadfast in your repentance, seek forgiveness, adhere to obedience to Allah, avoid the causes of sin, cut off the paths that lead to it, and beware of following the footsteps of Satan. You must turn the page on the sinful past and proceed on the path of righteousness, and fortify yourself with marriage whenever you are able to do so.