Black and white old movie about neighbors

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I’ve been dreaming about this old black and white 60’s movie I watched a long time ago.

About neighbors in a building, she used to go visit him via a service lift. He was rich but there was something wrong with her, either poor or her job that made her “questionable”.
I do remember being funny and kind of a romantic movie but the end was sad, like she thought he was going to end up with her but the last time she goes to his apartment he’s with someone else or something like that.
Both leader actors were big names and she was a short hair blonde.
Thanks for the help!

Gianna Asked question Apr 28, 2022