I just remember Irene is an actress I think and Seulgi is an idol. Irene gets jealous that at one point and then Seulgi gets jealous/upset because Irene is rumored to be with this actor and she's spending a lot of time with him. That's all I can remember. Thanks! 

I think it was part of a oneshot collection where Seulgi and Irene are wedding planning. Seulgi is on her phone or something and Irene get's mad but they make up because Seulgi apologizes.