Joke answer? Murdercock seeks the largest prey.
Honest joke answer? >Turn ons include: mature fun, equality>Turn offs include: grim maturity, childishness, clowns, childish grim clowns
The biggest clue is how dismissive she is of Greg early on. Saying it was fun to play with him in her song, laughing when against all odds and advice he sincerely attempted to gain a closer connection on her terms. Pearl outright saying he’s a passing game she would soon forget, all implying she treated her human lovers like a string of Spinels.
But Greg kept at it. He was a nice guy but wasn’t dumb. He began a bit more emotionally mature in how he approached relationships, but they were ultimately both young adults who learned together what it meant to actually be in a serious and stable adult relationship.
Garnet and Pearl’s reaction to it all is actually a good rebuke of people who say Fusion is only a metaphor for sex. To Pearl, Fusion was the pinnacle and end goal of a relationship, but remember that she sees Fusion as a means of escaping herself into the identity of her partner until much later. Garnet saw romance as romance, with Fusion just a Gem-specific means of connecting to each other among the many other ways, despite literally being “the Fusion Gem”.
Garnet knows this, even if her teenage parts have to learn that talking is the life blood of a true relationship later on. That factors into what Garnet as a Fusion truly represents, a mature relationship. Something she recognized immediately in where Rose and Greg were going. In order words, she saw her own kind between them even if they couldn’t ever actually merge like her. Which she later saw in Stevonnie too, teaching them the same lessons the same way she learned. With the exception of “be good for each other rather than only good together” which Steven had to teach Ruby and Sapphire before Garnet could teach him with the proposal.