The Halo universe consists of many species. Humans, Sangheili, Jiralhanae, Yanme'e, Unngoy, Lekgolo, Huragok, Kigyar, Forerunners, Yonhet(to name the contemporary ones). With the war between the Flood(warped Precursors) and the other sentient species, which as a result lead to the Forerunner-Human War, and later events like the Human-Covenant War.. it's understandable that animosity exists between the respective species in the Halo universe in general terms. But I've wondered, if Humanity can make peace with the Sangheili among others, could interspecies relations occur. They wouldn't be able to produce offspring of course, but that doesn't mean that they couldn't happen. If you look at groups aligned with eachother, ie the UNSC/UEG, Colonial Administration & the Swords of Sangheilios.. or the Banished and some of the Insurrectionist groups, then I think it's a possibility. Working together in cooperation like that might create a atmosphere where members of a different species bond with one another, and even develop feelings for eachother. This would likely create some interesting political situations between the respective species, but such occurrences couldn't be denied. And depending on the factions, they might even promote such relationships. If for no other reason than to be used as propaganda of Unity between the former enemies in this time of tension post War..