During certain dialogues in main and side quests, you can choose dialogue lines with a Heart icon on them. If you always select those, they will lead to romances. An easy way to get this early is by doing the "Age Is Just A Number" side quest in Phokis (Grand Mount Parnassos sub-region). It requires you to loot a deer and bear, which are both found in the same region as the quest. When returning to the quest giver at the end of the quest, select the "Let Me Satisfy You" dialogue with the heart icon to get the "Aphrodite's Embrace" trophy after the resulting cutscene. Alternatively, at the end of Sequence 4 in the "Perikle's Symposium" main quest, you will go to a party and can sleep with Alkibiades. Select the "Let's Get These Clothes Off" dialogue with the heart icon after getting oil for Alkibiades.