Is what the questioner did considered complete adultery, and how can one repent from it, knowing that he swore not to return to this act?

Adultery (zina) is committed when a male organ is inserted, even with the use of a condom, and it necessitates the prescribed punishment (Hadd). Repentance is achieved by immediately abandoning the sin and forsaking disobedience, regretting what has occurred, and sincerely resolving not to return to the sin. A condition for the acceptance of repentance is that it must occur before the death rattle (ghargara) and before the sun rises from the west. Repentance should be followed by righteous deeds that remove the effects of sins and transform them into good deeds. Allah, the Almighty, says: "Indeed, good deeds do away with evil deeds." [Hud: 114], and He says: "Except for those who repent, believe and do righteous work. For them Allah will replace their evil deeds with good. And ever is Allah Forgiving and Merciful." [Al-Furqan: 70]. Among the acts by which Allah erases sins are performing ablution thoroughly despite difficulties, taking many steps towards the mosques, and awaiting one prayer after another.