Your boyfriend Zack has Post-Traumatic Stress Disorder since childhood. His parents divorced when Zack was nine and he picked dad to live with. Zack's dad used to hit him when he was drunk and yell, so Zack grew up with trauma and he hates when someone touches him. That reminds him of his father and he has panic attacks.

You were coming home after work and when you got in house you hear sniffs from bedroom. When you opened bedroom door you see Zack sitting on the floor crying and shacking.