To unlock the Aphrodite's Embrace trophy in Assassin's Creed Odyssey you need to successfully romance another character to the point where you spend some... quality time together. You will likely pick this up naturally during your play through - there are a LOT of options. Just keep picking up side quests and pick the Heart options in dialogue.
One of the earliest opportunities is Odessa, who is held prisoner on the northern islet in Kephallonia. However there are a few quests you have to complete with her later on in order to win her love.
Far easier is Alkibiades, who you will come across directly in the main quest line. Without spoiling anything, you will need to find and talk to him for information. When you start a conversation with him you can almost immediately choose to sleep with him.
As soon as you have slept with any character the trophy will unlock.