One of the pieces of evidence some religionists like to toss around to "prove" that humans are not mere animals is that we humans are the only species on the planet that mates face-to-face. What they don't realize is that many other animals mate face-to-face, including woolly spider monkeys, bonobos (pygmy chimpanzees), and orangutans.
Copulation and ventral-ventral are the preferred scientific terms. I always correct my primatology students to use the term ventral-dorsal when they refer to the more usual animal mating position: doggy style. There are always a handful of students who have a difficult time making the switch. Those students also have a tendency to say animals "have sex." They don't. Animals mate or copulate. If they're going to learn how to approach the subject from a scientific perspective, they have to talk like scientists do.
But back to the story - of what significance is this gorilla observation? The primatologist who made the observation, Thomas Breuer, is hesitant to draw any conclusions, which is wise, given that this is a one time observation between one pair of gorillas — not a widespread pattern typical of adults.
Psychologists speculate that ventral-ventral copulation might engender a deeper relationship between a mating pair. It affords prolonged eye contact, something that has been scientifically linked to greater pleasure, liking, and even love (among humans). Perhaps this happens with other primates as well.
Breuer observed the gorilla pair mate for about 2 mins., after which the silverback briefly held the female's hand. Even the world's largest primates, of King Kong fame, enjoy affection. "Maybe there's a way the act forms a kind of bond between the silverback and the female," Breuer says. "But we just don't know."
Documenting internal feelings of love is challenging, whatever the species.