Her sexual practices, fidelity, intimate life, etc. *may* impact on custody but doesn't have to. Custody is about the best interests of the children, not about punishing a cheating spouse or expessing moral disapproval of her life. If as a result of her lifestyle or relationships, your wife can be shown to--1) Bring unsuitable partners home and expose them to her children;2) To expose her children to inappropriate behavior;3) To neglect her children; 4) Etc.--then this may lead to you getting full custody. But if she is a good mother and keeps her private life separate from her children so that it doesn't affect them, then it is likely to have very little bearing on custody.