[Does hold back at first. At least, he tries to - that mounting feeling of losing his control is a little terrifying, honestly, even with Victor's hold grounding him.
When it does become too much, his first reaction's almost involuntary, clinging so tight to Victor's back that his nails break the skin and he starts to writhe in pain, and doesn't start screaming only because he shifts up and presses his face into Victor's neck and bites down hard.]