Is ejaculating semen onto the anus without penetration considered adultery, and is a woman's fear that her pregnancy is not from her husband, after her repentance and five years having passed since her act, considered a divine punishment?

What happened is not zina (fornication/adultery) that necessitates the hadd punishment; rather, it is a forbidden and reprehensible act. Allah accepts repentance and pardons sins. So, as long as you have repented, rejoice in Allah's pardon, and do not pay attention to the whispers of Satan. Occupy yourself with what benefits you, turn to your Lord with acts of obedience, have a good opinion of Him, and increase in supplication (dua) and remembrance (dhikr).