How can one be sure of the acceptance of repentance after abstaining from sin was not initially motivated by fear of God, and what is the way to deal with negative feelings towards someone who inflicted psychological harm?

Your repentance – God willing – is accepted as long as you are regretful and determined not to return to the sin, even if the repentance occurred after separating from the man. For, according to the Sunnis, the repentance of one who is unable to commit the sin is valid, as mentioned by Ibn Taymiyyah. The fear of non-acceptance and diligence in acts of obedience that you experience are signs of the acceptance and validity of repentance. Among its signs is that a person becomes better after repentance than they were before, and that a continuous fear of Allah's cunning accompanies them until they hear the words of the angels at the time of their soul's capture: {Do not fear and do not grieve, but receive good tidings of Paradise, which you were promised} [Fussilat 41:30]. Another sign is the breaking and tearing of the heart from regret and fear. One must be wary of satanic whispers that remind of the sin, for true repentance necessitates that the heart does not turn to it. Weak resolve and remembering the sweetness of sin are accusations against repentance. To overcome these whispers and remain steadfast in repentance, seek Allah's help, frequently supplicate to Him and remember Him, and occupy your time with beneficial matters.