Oh, it did happen. Arthur gets jealous easily, and Porthos doesn't but he did get jealous of Arthur and... [And Anne.] And someone else, who I think had a lot of trouble learning about all of this.
But... Even if it's complicated, it doesn't make it much different than anything else. You could be with just one person, and they could get jealous too. It could be exhausting to be with them alone, too.