No. After they establish a relationship they don't sleep around.
Spoiler
Before they become official, the seme is implied to be dating multiple women even some at the same time. However, he's doing this to use them (get info from them, get connections/ power) so he can fulfill his plan to take revenge on someone who killed his family. We mainly just see him going on dates w the women and one or two not detailed at all sex scenes which got cut off cuz he was confused about his feelings for the uke (since he's been a hetero all his life and they're in the 80s-90s). The uke suffered a lot emotionally due to this but at the same time, I'm not that mad at the seme since all his life, his main purpose was to just use ppl for his revenge and throw them away when they become useless but the uke came in and changed that. In the end, they have a satisfying and happy ending. It's definitely worth a read. One of the best pacing, plot and character developments in bl stories.
Before I start reading this can someone give me an explanation of the main characters relationship and if cheating (physically or emotionally) is ever involved? Even if it’s not technically cheating, do we see either characters sleeping around with other people? This is something I’m very particular about and i’d rather know what to expect before driving into such a long story. Spoilers pls!! Thanks