Why can't my ex spend time with his son without his girlfriend in the picture?

There could be several reasons for this situation. Your ex may feel more comfortable or secure having his girlfriend present, possibly to avoid any awkwardness or tension. Additionally, he might believe that his girlfriend's presence enhances the experience for their son or provides support during their time together. Ultimately, it may reflect his current relationship dynamics and how he chooses to blend his personal and parental roles.