
I think a more accurate comparison would be to say that the dog was unfaithful for eating meals at another person's house... obviously that would be stupid cause eating a meal is not something worth fidelity. I think the point this person is making is that the seme deserved to loved as something a little more than just a meal... the uke obviously places no emotional value on sex given that he slept with everyone who came to the Cafe... and I don't think the manga resolved that emotional distance... however if you are going to read a Manga about a sex demon you have to be prepared for them to not think of it as anything other than a meal...
A side point is that a demon that feeds on sexual energy is pretty much by definition a slut... and would probably be proud of that... so your point is kind of mute anyway, the bigger question is whether sluts make good lovers

No, the definition of a slut is not a person that needs sex to survive, I am sorry but you are mistaken. Slut is a person that thinks very casually about sex and does not consider monogamy. In this case a) the uke needed sex to survive, not for fun b) if you remember the chapter where his mother had a druged minotaur easy for him to feed but he preferred to "starve" c) from the moment he saw the seme he was thinking constantly about him and start feeding from other people. But if we agree to believe the story frame it is his life on the line, not his carnal pleasures. So no, he is not a slut. And that was proven so much at the end when he break off his horns (so he would stop being a magic being - having to feed via sex). He chose to live and love as a human so he wouldn't have to have sex with others or kill his partner in order to survive. Now about the theoretical question you pose about sluts and relationships... Well the answer is again on how you define a slut. A person having a rich sex life is not a slut. Maybe he/she haven't fall in love yet. Maybe it is a phase in their life. If they are clear on what their doing they are ok. And maybe in the future they will find someone to love and cherish. Now if a person while forming exclusive relationships is always unfaithful and seeks sex constantly, yeah they are a slut and probably not good relat material
Eveyone acting like this was good but this the same old shit about a slut who has sex with everything on two legs masked as him being an incubus. The first story was shit. The seme deserved better