My partner was murdered approx 17 months ago by his son, and i am worried that i have no anger/emotion towards his son and can't seem to move forward?

More therapy: You must get help with this. There are so many possible reasons that you are not feeling angry and not moving on. You list that you have had psychological treatment. You need more therapy to help you process this violent loss that you've experienced. You might also want to consider a support group. Good luck and best wishes.

Talk to wise people: How you feel or do not feel about your loved one's killer is not the key. However, you must get on with your life from this point. This will involve talking with wise people ("therapists" or lay guides) about what you are able to do (rather than how you are hurt), what is still intact, what is still yours, and how you set even limited goals for a return to a normal life.

Emotion: Emotional numbing can occur often as a response to extreme trauma. An example would be a combat veteran returning home and feeling nothing at the death of a loved one. People with schizoid personality disorder are indifferent to interpersonal relationships and appear to be emotionless, often. These are just two examples, there are others.