I don't necessarily mean a uke who cheats on his partner,though I have no probs with this recommandation if you know some.
It should be more because he is confused,or the seme and him broke up at one point so he tried dating someone else.
Oh and I prefer it to be a rather long story (even a couple or chapters are fine but please no oneshots) and I'd like my uke non feminine and not annoying (the type that cries for nothing gets on my nerves).Also,the sex "affair" has to be fully consensual.

You can try Walker series from Miyamoto Kano.

Edit:
Oh, by the way it starts with Not/Love, first story author wrote in this series.

Like in Totally Captivated ! 😲

Don't Cry Baby is pretty good, and fits.

Aisanai Otoko too.

Neither is super long, but not one shots.

Thank you but I've already read those 😔
Any other suggestions ?