Divorce

I have decided to file for divorce. I've been with my husband 15 yrs total and only married for 5 yrs. I have a son from a previous relationship, he has a daughter from a previous relationship and we have a child together. His daughter is very problematic and irresponsible, just turned 18 and does whatever the heck she wants. My son is no angel but does not drink, smoke or do drugs like her. Last week she let a guy sleep in our living room. I had only seen him once previously. I have a 10 yr old to worry about. When I kicked out the guy my husband undermined my authority and told him he could stay. When I told him that I would file for divorce if he didn't tell that guy to leave his reply was "good". He thought I was not serious and was surprised to see he now has to share a room with his daughter because I moved my 10 yr old into my room. When his daughter is gone everything is fine but she comes and everything falls apart. She plays the victim and he believes her. He's even kicked me and my two children out (in front of them) to "protect" her, when all I do is avoid her. I know that I did what I'm supposed to but I feel so alone....