I do understand your dilemma.
First of all, I have learned that 'forgiving' another person is NOT for that person but for myself. It does not mean that I will forget. It does mean that I ACCEPT that the person is very sick. 'Forgiveness' allows me to drop the 'resentment' and continue my own healing process.
There is a 'line' in "The Lord's Prayer":
"Forgive us our trespasses as we forgive those who trespass against us."
Now I am not a 'religious' person, but I do try to live a 'spiritual' way of life. That line is ME asking HP, the universe, The Great Spirit, whatever I do believe in to please 'forgive' me my trespasses/sins as I forgive those who trespass/sin against me.
Boy was that a 'heavy' one for me to digest. I had to ACCEPT that my continued 'resentment' against the person was only HURTING ME and KEEPING ME in a dark place.
So ............................ forgiveness is not about what your AXGF did to you, it is about the 'resentment' that has and is forming, which puts you in a dark place and covers up the sunlight getting to your inner self.
If need be, do some journalling about this to work on your own ACCEPTANCE that she is a very 'ill/sick' person. Give that 'acceptance' to your own HP, the Universe, or whatever you believe in.
It does work honest. When the 'acceptance' comes, the resentment leaves.
Hope that helps a little bit.
Love and hugs,