My take on it when I read is that Seme didn’t cheat on Uke with red hair. His emotions and stuff didn’t feel deceiving to me. He was genuinely confused and that’s why he questioned why Uke would think that far of him.
I also think so too, it's just that cause of the Uke's past relationship they're actions (the Seme and his ex's) were the same, that's why he thought he was cheating on him, and since the Seme is originally straight. But I don't think that the Seme would actually do that. Idk ╮(￣▽￣)╭ let's just wait for it to unfold.
i believe seme wouldn't cheat on uke even without the spoiler, but they do take their sweet time everything a misunderstanding happened
So based on my understanding from the raw from chapter 56 to 57. The Uke confronted the Seme about this matter but the Seme refuse to tell the truth for it concerns someone's privacy (or so that's what google translate said), the Uke got angry and got some backlash of his past relationship with straight guys saying the same excuse blah blah blah and then the Seme said "do you not trust me" which made him more angry? (Idk if that's the right emotion to use but something like that), then the Uke got some back flash of his ex saying the same thing and blaming him for misunderstanding the situation etc. etc. Then he walked out of his car the Seme chase him trying to explain things to him and say that they're just acquaintance?. And then the yellow haired guy (the one who tattooed him) came and interrupted them, then the Seme go to the car and drove away. Then after that, the next morning in the office, they ignored each other and then the i don't know his name guy (the one who he suspected that the Seme cheated on) came to him and spoke to him about their relationship, and at the very last panel he said that they were just business (i don't know what that means, since i just translated it from the raws to google translator) that's where chapter 57 ends which is the latest chapter in the raw.