For some this is the way to go about First Contact.Alien invaders seemingly love to tempt humans with this as part of their Masquerade, although you'd think they'd learn better.
In less realistic settings, can easily result in Half Human Hybrids or Hybrid Monsters, or even Random Species Offsprings.
"Debbie Reynolds (in 'Singin' in the Rain') reminds me of Piggy when I first met her," he said. Reynolds."Before long, Miss Piggy and Kermit were dressed in their best wedding wear and ready to walk down the aisle on "The Muppet Show." Piggy tricked her Kermie into it by presenting their wedding as nothing more than a sketch for the variety program while secretly hiring a real minister to officiate.
Kermit managed to evade saying the magic words -- "I do" -- and earned payback from the pig.
May lead to Half Human Hybrids or to a Non-Human Lover Reveal if one member was keeping secrets.
If society does not approve of such romance, then it's also Maligned Mixed Marriage.