The boyfriend is being unreasonable! The girlfriend is paying for the subscription with her own money, and it brings her joy. It's not about the money, it's about the tradition and the connection to her father. He should respect her hobbies and stop being so controlling.
This is classic financial irresponsibility disguised as 'tradition.' She admits she could use the money for something else, but she's too stubborn to compromise. He has every right to be upset about her wasting money on something so trivial, especially when there are free alternatives. It sounds like she refuses to grow up.
While it is her money, the boyfriend's concern is not entirely unfounded. The girlfriend's unwillingness to even consider alternatives does suggest a lack of compromise. However, the boyfriend should respect her hobbies. Thus, some compromise on both sides would be ideal.