After reading fics written by romanoff and somanyfeels, it remind me of this fic posted at ao3 (last year, i think) where Tony broke up with Steve because Steve spent too much time Bucky. Bucky and Steve was not in a relationship. I remember Steve forgot/cancelled many dates including their anniversery date. Tony talked to Steve about this and Steve promised not to do it again. But after few months, he did the same thing again till Tony fed up and broke up with Steve.
When Bucky dating Natasha, he began to ditch Steve to spend time with Natasha. Now, Steve know how it feels like to be neglected