What is the ruling on my envy in this situation, and am I an oppressor or oppressed, knowing that I do not pray and that my husband is having an affair with my aunt and justifies it by saying that I am not his wife, but he has not divorced me?

Abandoning the obligatory prayer is one of the gravest evils, and its sin is greater than the sin of murder, adultery, theft, and drinking alcohol. Therefore, the questioner should hasten to sincere repentance and remain steadfast in obedience to Allah, in order to live a happy life in this world and the Hereafter.