Yo

Have you read the novel or are you just guessing based on comments . Seme had 9 concubines who were killed . And he no longer felt the need for sex as cooling off steam but he felt a need for oneness with uke .....there was no mentioning whether he had concubines after his relationship with uke and whether he was interested in them. Someone just said in comments that seme was seen with another woman after sensing jealousy and betrayal because of uke...and that comment said he was not even sure whether he slept with her

Besides ....assuming if it's true he cheated...then it might not be cheating in a sense of breaking commitments because there was no demands from uke .....but it's still cheating cause seme claims he loves uke but does something to hurt uke. Just because uke never complains doesn't mean seme was justified not to have noticed his beloved grief.....it's cheating of one's feelings not cheating based on business like agreements

I did not read the novel( and do not hold its importance) my opinion was solely based on what ive read on the site.

So far i didnt see any remark by seme that yuer is the one he loves and hes not going to sleep with any of his concubines ( there are various royalties mangas where the kings have forsake their concubines after meeting the "one") since it isnt mentioned here i did not see any fault in him 'if' he does ecer sleep with someone.

Your opinion is illogical because cheating doesnt only equate when feelings are involved.
Suppose a married couple (who doesnt love each other) and one of the partner cheat on them with somone else, would you justify and say its not cheating because the couples didn't have feelings for each other?
i still stand by what i said, i would not call it cheating if the seme sleep with someone other then yuer( same with yuer) simply because they never actually committed to not sleeping with someone else ( again there are many royalties manga where the king have mentioned not to sleep with someone else after falling for the uke, this many seem little to no importance but its a statement of his commitment to the uke)

If the prince continues with his lecherous ways and sleep with others it will hurt shenyu and it did greatly in the novel. That is cheating . Not in a sense of breaching the contract in a business like relationship,
the kinda of marriage you said is a business relationship like that of Victorian era marriages, Besides just because you didn't see prince confessing his love or commitment, doesn't mean he didn't intend to. Remember the prince is a selfish tyrant who doesn't know love and is too arrogant and insecure to admit it .
The irony here is that prince beats shenyu if he suspects shenyu of cheating but he himself goes to sleep with a prostitute only to punish shenyu. I wouldn't hesitate to assassinate such a prince

You're treating the prince based on Modern day , post sexual revolution relationship ethics which treats love and dedication as a contract and it treats subjects such as fidelity as something not innate but something acquired....whereas in the traditions and context of most manhwas and mangas the relationship ethics knows fidelity as something innate .

I don't know about fidelity but doing something which would make your claimed feelings insincere and would hurt your beloved is cheating of one's love claim. Worse is when you want your beloved not to do a thing and you would beat him if he does it ,but you yourself do that very thing.
The prince does all of this ^