Split them up?

my partner arrived home with another woman. We had been together 6 yrs and i still adore him. I had to leave as it was his flat and now she has moved in. Neither of them seem to care about my shock and heartache. I rang my ex to sort out some joint property and he said to come to his flat.He is ok on his own but when she is there she shouts over me and he shows off in front of her. I went to his flat and she was there they made fun of me , then she aulted me. He helped me but she was horrible, she is very common. She doesnt care at all about what she has done to me. She knew he was with me when she came home with him. I feel distraught. Any sugestions as to how i can split them up and give her some of the pain she has given me