How do I convince my husband, love of my life, that his mother is killing our relationship?

We are both on our second marriage with 6 kids between us, although none living with us. Three years ago my husband's father died. Within a month of his death my mother-in-law was saying she was unable to live alone.
As we were not in a position to have her move in with us, and with the last of our children having left, we agreed to move in with her.

Things were okay at first but have gotten steadily worse. The situation has changed the shape of our marriage (previously very happy) and I just want out of here.

How do I resolve this without having to make my husband choose between us and his mother?