Yeah, almost every relationship on Babylon 5 was monogamous. But this is supposed to be taking place in the future and one would think that there would be many different kinds of relationships between humans, and between humans and aliens. Monogamous, three-way, four-way, etc. There would have been different kinds of sexual orientations: straight, gay, lesbian, bi-sexuality, pan-sexuality, etc. We've seen sparks of something more between Ivanova and Talia and that episode where Marcus and Franklin went undercover as a couple on honeymoon but we didn't get more than that and explore it in more detail with the characters. Think Captain Jack Harkness from Torchwood and the future he comes from.
Maybe that's another thing that would separate the remake from the original and which the remake could benefit from.