The relationship between a mother and a son is a very special one and is also very important for a happy family life. A mother wants to see her son happy and with a good wife, and a son wants his wife to get along with his mom and respect her, especially if he favors her over his other family members.
This was the case for Reddit user RoadIsland123, who married a man whose mother favors him over his other siblings. While the wife understood this was wrong, she believed that if she could get along with the mother-in-law, she could fix the situation.
But after she tried and failed, she decided to leave her husband. More info can be found in the thread.