Basically the 2 protagonists find their significant others cheating on them with each other and these 2 get together (pretending to cheat) because of that but end up falling for each other.
http://www.mangago.zone/read-manga/nisekoi_doumei/This?
Yes! Thank you so much :)
Basically the 2 protagonists find their significant others cheating on them with each other and these 2 get together (pretending to cheat) because of that but end up falling for each other.