The plot was two old classmates who worked in the same office. One was being stalked and annoyed by a crazy woman and he used his old classmates as an excuse, saying that both of them were dating but they hadn't spoken for ages
sounds similar to this one, but they're still close, unless it's not this one
https://www.mangago.zone/read-manga/koibito_keiyaku_chuu_ni_tsuki/
As much as of an asshole he was, I won't blame seoan. Him crashing out is totally valid taking into account all the context.