it was pretty short like a few chapters long.
It was about two exes who met coincidentally at an onsen where each one went to with their current partners, and I remember the seme was with a girl, and they both cheated on their partners there
I’m not sure if it’s the right one but is it this one that you’re looking for??
https://www.mangago.me/read-manga/retsujo_love_cross/
Is it any good? Or is it another isekai manhwa?
It is an isekai, but a good one. The art is unique and there are some new story elements not commonly seen in these types of stories