Alliance

1. Dangerous Love: Get a Stormwind Guard's Card and return it to Aristan Mottar in Stormwind. To get a Guard's Card, put on some cologne or perfume and give a Love Token to an NPC who is looking for love. It may take a few attempts to get one of these as they may reject you or give you some other goodies.
2. Aristan's Hunch: Bring 1 Cologne Bottle and 1 Perfume Bottle to Morgan Pestle in the Trade District of Stormwind. This is simple enough, just run to the nearby Innkeeper and pick up a bottle of each. They cost 25C each.
3. Morgan's Discovery: Return to Aristan Mottar outside the bank in Stormwind's Trade District. Upon completion you will be able to choose a Box of Chocolates, a Handful of Roses or a Love Rocket as a reward.
4. Tracing the Source Speak with Innkeeper Allison at The Gilded Rose in Stormwind's Trade District.
5. Tracing the Source Speak with Evert Sorisam at The Finest Thread along Stormwind's Canals.
6. The Source Revealed Find Apothecary Staffron Lerent in the Hillsbrad Foothills behind Ravenholdt Manor. This guy is a little hard to find. There is a good map on Wowhead

Horde

1. Dangerous Love: Get a Guardian's Moldy Card and bring it to Fenstad Argyle in the Undercity. To get a Guardian's Moldy Card, put on some cologne or perfume and give a Love Token to an NPC who is looking for love. It may take a few attempts to get one of these as they may reject you or give you some other goodies.
2. Fenstad's Hunch: Bring 1 Cologne Bottle and 1 Perfume Bottle to Apothecary Zinge in the Undercity's Apothecarium. This is simple enough, just run to the nearby Innkeeper and pick up a bottle of each. They cost 25C.
3. Zinge's Assessment: Return to Fenstad Argyle outside the bank in the Undercity. Upon completion you will be able to choose a Box of Chocolates, a Handful of Roses or a Love Rocket as a reward.
4. Tracing the Source Speak with Innkeeper Norman in the Undercity.
5. Tracing the Source Speak with Mara Rennick at the tailor's shop in the Undercity's Mage Quarter.
6. The Source Revealed Find Apothecary Staffron Lerent in the Hillsbrad Foothills behind Ravenholdt Manor. This guy is a little hard to find. There is a good map on Wowhead