Define: trauma

• injury: any physical damage to the body caused by violence or accident or fracture etc.
• an emotional wound or shock often having long-lasting effects

With this in mind you have to ask what sort of shock found upon infidelity. Are you expecting long-term affects from this? If so it's possible, but in all truthfullness not likely. The hurt feelings and distrust resulting is very damaging but it's not along the same lines of verbal or physical abuse in a relationship which does often lead to PTSD.