The one that two-times can be either the seme or the uke.

BUT he should "two-time" with a girl, not with another man ( and he should still date both of them at the same time , not just just one of them then, then dump that person and go out with the other one).
I guess i prefer when the two men/boys stay together at the end ( i don't like dramas and tragedies!).

Thank you in advance !!! 🙂
Any help will be gratefully welcomed (^o^)/

Ubawareru Koto Marugoto Zenbu is all I can think of right now

Thank you a LOT @xxxillusionxxx !!!!!!! ^O^

I just finished reading "Ubawareru Koto Marugoto Zenbu" and i found it so entertaining ! Not only did it have the "two-timing-relationship" i asked for...but also the seme and the uke...they were just my taste, so to say ( = girly seme and kinda-manly uke>.<) hahahahaaha....And the art...just WOW ! 🙂
Thanks a lot, you just made my day ! 😀 😀 😀 😀

If you remember other please feel free to tell them to me 😀