Is there a sin for which God does not forgive its doer for a long time or ever, no matter what he does, and how does a servant know God's pleasure or wrath?

Allah has legislated repentance from sins and promised to forgive them. The only sin that Allah does not forgive is associating partners with Him (shirk), if a person dies upon it without having repented from it. As for sins less than shirk, Allah forgives them for whoever repents from them, provided the conditions of repentance are met: sincerity in repentance, regret, abstaining from the sin, resolving not to return to it, and that the repentance occurs at a time of acceptance (before the soul reaches the throat or before the sun rises from the west). Additionally, restitution must be made if the sin involved a transgression against a human being. It is incorrect to say that Allah does not forgive certain sins other than shirk, for Allah has commanded repentance and promised forgiveness. The exact time of Allah's acceptance of repentance is known to Him; He may accept it immediately or delay it due to His wisdom. A person should repent and be persistent in seeking forgiveness, and have a good opinion of their Lord. The sign of Allah's pleasure is being guided to obedience, and the sign of His wrath is loving disobedience and not being guided to good.