Not short but...
https://www.mangago.me/read-manga/the_third_ending/
This is what I thought of after reading your post. The darn picture pop in my mind lol. I love seeing the seme's crying face too ahhh so unforgettable
Here when one start catching feeling after one is with other person -
https://www.mangago.me/read-manga/kataomoi_to_parade/
https://www.mangago.me/read-manga/itsuka_no_koi_to_natsunohate/
is there any bl mangas (the short ones) where one has a crush on the other but then after a while stops trying so the other one starts catching feelings.
or
the one that has feelings starts hanging out with someone else and the other starts getting jealous