I never found it useful to communicate that i was doing it, and explaining one last time why i was doing it.
A "don't call, write, text, or email me anymore, and don't come by my house or the police will be involved for harrassment" worked well for me. Actually, the police had to call him and tell him the last part. That's it, no explanation of what no contact is, no reasons why I was doing it... he refused to hear any of it anyways. No contact is for you, not for them. I didn't feel i owed him any more than I had already gave him.
Your therapist saying that, i think is bs. Like everything I do or say is supposed to make everyone around me as comfortable as possible? If i break up with someone, i'm obligated to sit them down and list the reasons why, because they 'deserve an explanation'? I don't think so. Assuming responsibility for how others react to my decisions and choices is co-dependancy at it's most basic form. Why a therapist would encourage that is beyond me.