My t was okay with my si when I first started seeing her. I was always very careful about how I did it and my si rarely changed (from what I used, to cleaning it up, all the way down to how I cut, like the severity). If there were times I felt like I was at risk to myself or if I did need medical attention, I had a safety plan in place. My t went along with this until I told her I was done with si. At that point, she began holding me accountable to when I would harm myself and we talked about it. This is when she wasn't okay with it only because she knew I was ready to change. She was a lot more vocal about how it's a poor coping skill and stuff, since by the time I was ready to stop si, I had learned many new coping skills that were healthier for me.

My advice to you is to not try to get a reaction from your t but cutting badly. Maybe share those feelings with him, or share with him why it surprised you that he thought it was an okay thing when you told him about it.