How can one get rid of committing a forbidden act (being alone with girls and exchanging kisses) that recurs despite remorse and attempts to quit it?

Sincere repentance is necessary, for sins are destructive, harden the heart,Distance one from God, and lead to greater sins.

Ibn al-Qayyim said that sins and acts of disobedience are harmful like poisons, and they are the cause of all evil and sickness in this world and the hereafter, citing the stories of our parents (Adam and Eve), Iblis, and the peoples of 'Ad and Thamud as evidence.

Among the punishments for disobedience in this world are: lack of success, corrupted judgment, hidden truth, corruption of the heart, obscurity of reputation, wasted time, repulsion of creation, alienation between the servant and his Lord, prevention of supplications from being answered, hardness of heart, eradication of blessings in sustenance and lifespan, deprivation of knowledge, donning humiliation, humiliation by enemies, tightness of the chest, affliction with bad companions, prolonged worry and grief, straitened livelihood, and mental anguish.

For repentance, one must cut ties with those who aid in disobedience, choose righteous companionship, distance oneself from that which incites desires, humbly supplicate to Allah for steadfastness, and increase in supererogatory acts of worship and reading the Quran.