I usually like to try to dismiss any societal conditioning I've had and to think about things rationally. I think so many of us have strong opinions about things, like various social etiquettes, which really don't make sense when we think about them critically instead of just taking them for granted.
So superficially, the idea of separating sex and love, and many sexual partners, appeals to me. After all, I reason, "sex is just a physical act, and love is...." And then the problems start. What is romantic love? It is possible to achieve without sex, but sex is definitely something that can lead to it. If you have sex with someone enough times it will be hard for you not to develop romantic feelings. It seems that love is induced through neurochemical reactions which are strongly influenced by sex.
This leads to another interesting question. Is it okay to have polyamorous relationships? In principle I think this would be fun sexually, and otherwise quite interesting, because you'd simultaneously be experiencing being with different people who will have different personalities, opinions, interests, things to talk about, etc. Of course, it only seems fair that if you should have five romantic partners, that each of them should also be able to have five romantic partners. Why should you be the centre of attention? And you may start to favour one or two of the partners. This is when jealousy issues, etc., come into play. Just being human, it's not practically workable.
That's what I'd also say about having sex with other people while in a serious relationship. In principle, it sounds nice. But just being human, it's not practically workable, except in a few very unusual cases.