I guess that the ban on real life examples is in order to prevent zoophilic tropers from anouncing their "romances" with various animals and similar squick.
But the story isn't as easy when we include prehistory. There are traces of Neanderthal and Denisovan genes in the DNA of many people today that suggest there has been some level of interbreeding netween Homo sapiens and these species when they still lived on earth. This finding often gets interpreted as a sign of hanky-panky between our ancestors and more archaic human species. However, we don't know in how far these "mixing events" were consensual or not - part of it may be due to this trope, but another part may be the result of human trade between neighboring tribes or even some form of rape or sex slavery.
(Historians imagine the interaction between "us" and our archaic cousins as having been similar in quality to later "culture clash" events like the colonialization of the Americas by European settlers, and in these events the newcomers from the more developed culture were often ... not so nice to the Indigenous people, to understate it a bit. So scenarios with slavery, forced assimilation and sexual exploitation are not too far-fetched. Only the abuse, if it occured, must have been less systematic as our species consisted of numerous scattered hunter-gatherer tribes at that time. Probably every simgle Homo sapiens tribe had its own policy in regard to treating archaic humans.)
To complicate matters even more, biological taxonomists aren't sure if such close relatives to us like Neanderthals actually were a different species. After all, at least some of the first-generation hybrids must have been fertile in order to pass down and preserve the "archaic" DNA up to the present day. This is normally considered impossible for the hybrids of two different species.
Finally, were Neanderthals, Denisovans and who-else capable of romance at all? Probably yes, at least within their own species, but we don't know for sure. Say, their brains should have been sufficiently developed for making complex one-to-one social interaction (like romance) possible. What they probably lacked in contrast to us was a large-scale group think that caused us to develop states, civilisations and so on - you may need this if you want to fly to the moon or commit a genocide, but it's not required for falling in love.
What remains is the question if we could communicate with archaic humans in a reasonable way - species-specific nonverbal cues may become an obstacle to a true cross-species romance. Heck, differences in nonverbal communication can make a romance very hard to achieve even within our species - think about different cultures, or autistic-neurotypical couples.
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To make a long story short, it is speculated that our ancestors have had interspecies romances with Neanderthals, Denisovans and possibly other hominins which had previously split off from our family tree about 500.000 - 1.000.000 years ago (a boderline case of speciation). We can see the result of very likely interbreeding in our own DNA, but we don't really know whether this was the result of romance or something more sinister.
Sounds more like a case of Memetic mutation than a good real-life example.