Does it feel like your teenager is outgrowing or has “moved on” from his relationship with younger siblings?

“My 15 year old son has recently become a lot more focused on his friends and is much less interested in engaging with his 12 year old sister. He used to play with her all the time and now he barely talks with her. He’s never mean, just distant. He laughs and jokes with his friends and girlfriend, but is more somber when he’s just with the family. It breaks my heart to see my daughter’s loss and our mutual realization that those days are the ‘olden days.’ Do you have any advice as to how to maintain the bond/support of a younger sibling who misses her ‘until now, best friend?’”