D&C 64

To the elders of the Church, the Lord said -

"I will that ye should overcome the world; wherefore I will have compassion upon you."  (Doctrine and Covenants | Section 64:2)

The focus being on -

"There are those among you who have sinned; but verily I say, for this once, for mine own glory, and for the salvation of souls, I have forgiven you your sins.
4 I will be merciful unto you..."  (Doctrine and Covenants | Section 64:3 - 4)

Even of the Prophet Joseph Smith -

"...he has sinned..."  (Doctrine and Covenants | Section 64:7)

Suggesting -

"For all have sinned, and come short of the glory of God..."  (New Testament | Romans 3:23)

It is with this preface that the Lord teaches a great principle -

"...I, the Lord, forgive sins unto those who confess their sins before me and ask forgiveness, who have not sinned unto death."  (Doctrine and Covenants | Section 64:7)

Where "sinned unto death" would be -

"....if ye deny the Holy Ghost when it once has had place in you, and ye know that ye deny it, behold, this is a sin which is unpardonable..."  (Book of Mormon | Alma 39:6)

I will leave this exactly at what point this is to the Lord.  Of forgiveness, the Lord continues to explain -

"My disciples, in days of old, sought occasion against one another and forgave not one another in their hearts; and for this evil they were afflicted and sorely chastened.
9 Wherefore, I say unto you, that ye ought to forgive one another; for he that forgiveth not his brother his trespasses standeth condemned before the Lord; for there remaineth in him the greater sin."  (Doctrine and Covenants | Section 64:8 - 9)

I interpret that "there remaineth in him the greater sin" suggests that without forgiveness, anger, and maybe hatred and a desire for revenge may destroy the spiritual progression of the harmed individual.  Where the offender may repent, if the harmed does not forgive, it may ultimately lead to spiritual destruction.  And then the Lord lays out the commandment -

"I, the Lord, will forgive whom I will forgive, but of you it is required to forgive all men."  (Doctrine and Covenants | Section 64:10)

I don't believe that forgiveness necessarily means that you become best friends.  In many ways, the best approach may be to avoid or flee the individual to avoid a rekindling of feelings.  In fact the Lord adds this counsel -

"...ye ought to say in your hearts—let God judge between me and thee, and reward thee according to thy deeds."  (Doctrine and Covenants | Section 64:11)

Leaving or placing your burdens on the judgement of the Lord many times brings peace and comfort.