Responses
You just described "Elektel Delusion" but it's a manga
https://www.mangago.zone/read-manga/elektel_delusion/mf/v01/c001/
beta
Any manga/ manhwa where 'A' is in unrequited love with 'B'. But then 'A' meets 'C' and and starts spending more time with 'C'. Then 'B' gets jealous.