Will masturbation affect the bone healing process of a hairline fracture?

Unlikley unless: You injure the fracture. I.E. The chemical and physical response in the body will not interfere with this. As with any physical activity the important thing is to have caution if there is pain or discmfort during or right after that activity.

No: Please forgive my frankness. Enjoying your body will have no negative consequences unless you do it obsessively and end up missing appointments and other things you need to be doing. One of the cults writes a lot of rubbish to scare men. The truth is it won't interfere with your healing or any other aspect of your health. Best wishes.