I don’t have a girlfriend, but I do have two songs I can post for this one. They’re relevant enough.
While I don’t have a girlfriend, I do have a “waifu,” Miyamori Aoi from Shirobako, also known as best girl of all time. And the song that immediately reminds me of her is the Andes Chucky ending theme, which she sang/hummed at multiple points during the show. And it was Aoi-dorable.
The other song relates back to an ex. She made the arbitrary decision that this was “our song” because she felt that “we needed a song.” To look at this somewhat optimistically, it could have been a far worse song based on her taste in music.
The featured image is from Shirobako.