You shouldn't bring up old relationships with your current partner.
Holden is taking his girlfriend to a park in the town he grew up in.
Holden wants to convey how great the park is to his girlfriend.
Holden recalls a fond memory he had in the park with an ex-girlfriend, but explains it in a way that doesn't reference her at all.
Holden mentions a fond memory he had a the park with an ex-girlfriend of his.
Holden's girlfriend appreciates the story and grows more excited about the visit.
Holden's girlfriend gets angry at him for talking about his ex and it ruins the entire visit.