What i have to do next ?

I married will be nearly 4 years soon. I am living with my wife, her two kids with a previous marriage, and her mum in her mum council property house. My wife always like to be with her mum all the time. I am getting fed up with this. Every single week end she stays with her mum and her sister.Her mum don`t even talk to me. I just want to leave this house and live my life seperate. I asked my wife let us find a new place for us, she said she will never leave her mum. Her mum can look after herself. The kids don`t come around me when my wife`s mum is around. I am getting so fed up and getting stress everyday. Every friday and saturday my wife, her mum and the kids sit in the living room till 1 in the morning. i am thinking to divorce her, or just leave her for ever to stay with her mum all her life. they don`t even work so lazy! I know she will not sign the divorce paper, What do i do ? Thanks for all replies!!!!!!!!