How can I tell my mom that I want to live with my boyfriend if she dislikes him?

The question implies that you care what your mother thinks. If you know why your mother dislikes him, consider that it probably is because your mother see the boyfriend's values as contrary to hers. A mother's natural tendency and heart is to see her child protected, no matter how old are. The older you get the more important values will be compared to personality attraction or good looks. That which is obvious to your mother now will become more obvious to you later. Try to understand why your mother does not like him. Ask her to specifically define the issue with the understanding that her opinion is important to you. Remember that the divorce rate for couples that live together before marriage is double the divorce rate of those who do not. Self control and waiting are expressions of true love toward a potential mate. When people do that which is not for the other's good, love has been set aside and selfishness has taken over.