Is a person sinful for feuding with his brother who sexually assaulted him in childhood?

The questioner should dismiss the matter from his mind and conceal it, fearing people's talk.

Regarding his brother: - If he did this before puberty, there is no blame on him, according to the hadith: "The pen has been lifted from three... and from the child until he grows up." - If it was after puberty, he has committed a great sin and must repent.

How to deal with him now: - If he repents, he should not be reminded, scolded, or boycotted, as Islamic law forbids turning away from each other and abandonment without just cause. The Prophet, peace be upon him, said: "Do not hate each other, do not envy each other, do not turn your backs on each other, and be, O slaves of Allah, brothers. It is not lawful for a Muslim to abandon his brother for more than three days." - If he does not repent and insists on the sin, then it is permissible to boycott and abandon him, especially if the questioner fears that mixing with him might lead to something forbidden.

Filing a lawsuit: - A lawsuit by the questioner without proof is considered slander. The punishment for a slanderer is eighty lashes if he does not produce four witnesses, as Allah Almighty says: {And those who accuse chaste women and then do not produce four witnesses - flog them eighty lashes}. A person may deserve flogging merely for alluding to such an accusation.