I'm looking for and idiom, expression or proverb for criticizing (or describing) a situation in which someone doesn't pay attention to/ like their old things, friends, colleagues, hobbies, etc any more just after having or finding a new one, and that might be kind of annoying to others.
We Iranians use a proverb that literally says:
"When the New comes to the market, the Old would become boring/ uninteresting."
It would be stated sarcastically in situations like these:
1- I have a 9-year-old daughter who loves her toys very much, especially her teddy bear. Some day, I buy a kids' tablet for her and after that she wouldn't pay attention to those toys any more.
When I ask her "why don't you play with the teddy bear any more!?" She would reply " Oh, I don't like it, I prefere to play with these apps." Then my husband would say "as you know, when the New comes to the market, the Old becomes uninteresting! (i.e. now that she has that tablet, she doesn't pay attention to/ like her old toys any more.)
2- I'm a high school student, and a beautiful and clever student has recently transferred to my class.
After making friend with her, I spend most of my time with her, so my classmate who was my best friend before, would sarcastically say to me "Oh, I can't belive it! I see that you have totally forgotten about me! Well, that's why that old proverb says "when the New comes to the market, the Old becomes boring!", okay! I have nothing to do with you either! Have fun with that new friend!"
Is there any idiom or proverb in English that could convey this connotation?
I have found "out with the old, in with the new" as equivalent for this Persian proverb in some Persian -to -English books, but I'm not sure if it would have the same meaning.