hi, im new here, ive had this manga stuck in my head for a while now but i cant anything except for one or two specific s 4pa1m

It was a high school manga about this guy and girl, i dont what their relationship is at the start but in the past when they were kids they were bery close, with the boy describing her as very beautiful even as a kid, captivating everyone around her. Then one night when he decided to look for her, he found a middle aged, balding salaryman going in and doing inappropriate acts with her, shocking the boy. After the man is done, the girl goes out to her balcony and looks at the boy, smiling. The boy then runs away and from there their relationship changes for the worse

towards the end in present time, the boy and girl run into each other at a bus stop while it was raining, and they end up doing it. Their relationship ends when the boy says that their relationship wont work out due to reasons i cant . He might have another potential love interest at this point.

all of this is based on my very shoddy memory. some potential tags might include drama, slice of life. any help in finding this manga will be greatly appreciated!