Why is it so hard to forgive myself?

...How does one confess? He states: "I implore You, God, I sinned, I transgressed, I committed iniquity before You by doing the following. Behold, I regret and am embarrassed for my deeds. I promise never to repeat this act again." These are the essential elements of the confessional prayer...

What constitutes Teshuvah? That a sinner should abandon his sins and remove them from his thoughts, resolving in his heart, never to commit them again...Similarly, he must regret the past...He must verbally confess and state these matters which he resolved in his heart.

(5) When you see the ass of your enemy lying under its burden and would refrain from raising it, you must nevertheless help raise it.

עזב תעזב עמו — The root עזב has here the meaning of “helping”...

...abandon what is in you heart against him and unload with him] .

(7) If your brother, your own mother’s son, or your son or daughter, or the wife of your bosom, or your closest friend entices you in secret, saying, “Come let us worship other gods” whom neither you nor your ancestors have experienced (8) from among the gods of the peoples around you, either near to you or distant, anywhere from one end of the earth to the other: (9) do not assent or give heed to any of them. Show no pity or compassion, and do not cover up the matter;

ולא תשמע אליו AND THOU SHALT NOT HEARKEN UNTO HIM when he makes entreaty for his life, that you should forgive him. This is stated because it says. (Exodus 23:5) “[If thou see the ass of him that hateth thee] thou shalt surely help him”; this man, however, thou shalt not help (Sifrei Devarim 89:2).

(10) It is forbidden for a person to be cruel and refuse to be appeased. Rather, he should be easily pacified, but hard to anger. When the person who wronged him asks for forgiveness, he should forgive him with a complete heart and a willing spirit. Even if he aggravated and wronged him severely, he should not seek revenge or bear a grudge. This is the path of the seed of Israel and their upright spirit. In contrast, the insensitive gentiles do not act in this manner. Rather, their wrath is preserved forever...

...If the Sanhedrin saw someone kill another person, some of them are rendered witnesses and testify before the others and some of them become judges in the case; this is the statement of Rabbi Tarfon. Rabbi Akiva says: They are all rendered witnesses, and a witness cannot become a judge...for the Merciful One says: “And the congregation shall judge…and the congregation shall save” (Numbers 35:24–25), which requires a court to search for grounds to exonerate the defendant, but once they themselves have seen him kill a person, they will be unable to find grounds to exonerate him...

...a witness may not serve as a judge. This applies even in cases involving financial matters.

...Rava says: A person is his own relative and therefore may not testify about himself. Therefore, a person cannot render himself wicked by his own testimony...

(2) A person is not disqualified as a witness because of a transgression on the basis of his own testimony. What is implied? A person comes to court and admits that he stole, robbed, or lent money at interest. Although his own statement is sufficient to obligate him to make financial restitution, it does not disqualify him as a witness. Similarly, if he states that he ate meat from an animal that was not slaughtered in a ritual manner or had relations with a woman forbidden to him, he is not disqualified until two witnesses testify concerning the transgression. The rationale is that a person is not deemed as wicked on the basis of his own testimony...

(13) Rabbi Shimon said: Be careful with the reading of Shema and the prayer, And when you pray, do not make your prayer something automatic, but a plea for compassion before God, for it is said: “for He is gracious and compassionate, slow to anger, abounding in kindness, and renouncing punishment” (Joel 2:13); And be not wicked in your own esteem.

(7) Then Moses said to Aaron: “Come forward to the altar and sacrifice your sin offering and your burnt offering, making expiation for yourself and for the people; and sacrifice the people’s offering and make expiation for them, as ה' has commanded.”

A Baal-Teshuvah should not consider himself distant from the level of the righteous because of the sins and transgressions that he committed. This is not true. He is beloved and desirable before the Creator as if he never sinned...for he has tasted sin and yet, separated himself from it, conquering his [evil] inclination. Our Sages declared: "In the place where Baalei Teshuvah stand, even the completely righteous are not able to stand." The level of Baalei Teshuvah transcends the level of those who never sinned at all, for they overcome their [evil] inclination more.

(12) When you have set aside in full the tenth part of your yield—in the third year, the year of the tithe—and have given it to the [family of the] Levite, the stranger, the fatherless, and the widow, that they may eat their fill in your settlements, (13) you shall declare before your God ה': “I have cleared out the consecrated portion from the house; and I have given it to the [family of the] Levite, the stranger, the fatherless, and the widow, just as You commanded me; I have neither transgressed nor neglected any of Your commandments: (14) I have not eaten of it while in mourning, I have not cleared out any of it while I was impure, and I have not deposited any of it with the dead. I have obeyed my God ה'; I have done just as You commanded me. (15) Look down from Your holy abode, from heaven, and bless Your people Israel and the soil You have given us, a land flowing with milk and honey, as You swore to our fathers.”

At minhah on the last festival day they would make the confession...

The commandment of declaration of tithes: That we have been commanded to declare before God, blessed be He, and to state with our mouths in His Temple, that we took out the legally required tithes and priestly tithes from our grain and from our fruits, and that none of them is remaining in our possession that we have not given...in any language...(a)fter the third year...on the last day of Pesach; and so [too,] in the seventh [year]...