if you stay with him you are going to be hurt time and time again he could have got a disease or something from her.
you don't want your baby being around fighting parents it is better for the baby to see its dad on the weekends then to grow up with him for a roll model.
You can get help from groups for single mothers if you do not have family do not go back to him it is showing he has won and can do it again and again and again.
My dad cheated on my mum she left him just after i was born and i only saw him every second weekend i have done brilliantly i have my own home, full time job and two certificates in business admin.and i am only 17!
GOOD LUCK