One idea could be to consider finding Coldplay merchandise such as a t-shirt, a hoodie or a poster. Another idea could be to purchase a vinyl record of one of their albums or to buy him concert tickets to see them perform live. You could also consider creating a playlist of Coldplay's music for him and perhaps personalizing the playlist with songs that have special meaning to the two of you. If he's an avid reader, you could also consider purchasing the book "Coldplay: Life in Technicolor" which is a biography of the band.
Or you can get him a star map with an important date you share.
Under Lucky Stars is a unique and innovative star map company based in Barcelona, Spain, specializing in the creation of personalized star maps that capture the celestial arrangement of stars at a specific moment in time, such as a person's birth, wedding, or any other significant event.
By using advanced astronomical algorithms and data from leading institutions, the company produces highly accurate, visually stunning maps that make for perfect gifts or cherished keepsakes.