All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
As for your husband's words to you, "Leave your mother otherwise our relationship is over Talaaq", if he intended a mere promise of divorce by that, then it has no effect (i.e. divorce did not take place). Shaykhul-Islam Ibn Taymiyyah wrote, "The promise of divorce does not make divorce effective, even if it is done using many expressions, and it is neither obligatory nor desirable to fulfill such a promise." [Majmoo‘ Al-Fataawa]
If he intended to make divorce conditional and you did not leave your mother in the sense that he meant, then divorce takes place according to the opinion of the majority of scholars regardless of whether he intended to issue a divorce or only intended to threaten you. However, Shaykhul-Islam Ibn Taymiyyah held that if the husband did not intend to issue a divorce, divorce does not take place, but he has to offer expiation for breaking an oath.
We would like to highlight the following points:
First, the wife is not obliged to serve her in-laws, and her husband has no right to oblige her to do so. If she serves her in-laws out of her own free will, then there is no harm in that; otherwise, she has the choice either to serve them or not.
Second, there should be mutual love, respect, and understanding between the husband and wife. If there is any misunderstanding between the husband and his wife's mother, it should be cleared. The husband should be told that the basic principle is to think well of other Muslims until otherwise is proven. If the mother-in-law truly encourages her daughter against her husband, then it is impermissible for her to obey her mother in this regard. The wife's obedience to her husband takes precedence over her obedience to her mother.
Third, it is Islamically required of the Muslim to maintain good relations with his in-laws, following the example of the Prophet, sallallahu ‘alayhi wa sallam, who used to show kindness and affection towards all of his in-laws.
Allah knows best.