Your wife is likely having an affair. When you let her come and go at all hours, you are disrespecting yourself, and it portrays WEAKNESS to her. Weakness is not attractive to a woman, since they tie their feelings of "love" for us very closely with their feelings of "respect."
What are your boundaries? (if any) What (if any) were the consequences for her the first time she came home at 3 or 4 am?? What if one of your daughters woke up at 3am and needed her mother?