Now I'm curious what's his deal in going with other girls except her? Since he love her enough to hide the evidence.
It's practically a trope: shopping for her present - he wanted a female opinion.
Every time he takes a friend along to help him pick out a gift for his yandere girlfriend, she thinks he's taking another girl out on a date. After letting the misunderstanding go on for years without ever confronting him for an explanation, she finally reached the point of "If I can't have him, no-one else can."
While he was shopping for an engagement ring to propose to her on Valentine's day, she was planning to murder him with chocolate.
Communication is important in a relationship.