Lampshaded: "Um... Bob... most people try to only romance people of their own species, you know."
Invoked: The females of one species are designed to be sexually attractive to the males of another species (or multiple other species), either for reproduction or to serve as a hunting lure.
Exploited: Knowing his love for werewolves, Emperor Evulz sets up Bob with Alice to both distract him and have Alice relay information regarding Bob.
Defied: "Yuck, I don't wanna date a werewolf!"
The happy couple take the time to work out cultural differences, overcoming biochemical barriers, and managing mechanical differences between Tab A and Slot B.
An interested third party who has researched both species offers some helpful advice on managing cultural differences, and warns of any activities that would normally be safe if Bob was dating a human, but could be potentially dangerous or painful under the circumstances.
Conversed: "Why do humans and non-humans keep falling in love in these books? You'd think the dietary concerns would be enough to keep them from having anything meaningful."
Deconstructed: The differences between Bob and Alice's species threaten to tear them apart, literally. Bob stumbles upon Alice, who has transformed fully and isn't in control of herself, and is attacked by her.
Reconstructed: Bob, after dating enough dangerous creatures, expected this to happen at least once, and came prepared. After the incident, Bob still loves Alice.