The problem with Instagram blocking is that if you have a public profile on there, he can still see it on a web browser if he really wanted to. It only blocks people who are logged in on the app, not the public at large.

Also, in case you didn't know this, Instagram has a policy against photos that show self-harm. If someone reports your photos for that, they will remove them and send you a message offering you resources for mental health and crisis counseling. Just thought I'd mention this.