Fans of the Star Wars Original Trilogy may be surprised to learn that, in the Expanded Universe, Luke Skywalker is quite the ladies' man. His combination of farmboy charm, Jedi powers, and boyish good looks seemed to make women fall instantly in love with him. Few of his relationships got off the ground, however, and most of those that did were doomed to end in tragedy.
Princess Leia was Luke's only love interest in the Star Wars films. His attraction to her began when he saw R2-D2 project her holographic message to Obi-Wan Kenobi. At the end of A New Hope, there was some tension between Han Solo and Luke with regards to who would pursue Leia's affection; Luke assured Han that a smuggler like him would have no chance with a princess.
Luke and Leia flirt with each other in the early EU works Marvel Star Wars and Splinter of the Mind's Eye, although when Leia kissed Luke in The Empire Strikes Back, it seems she was only trying to make Han jealous. Regardless, the revelation in Return of the Jedi that Luke and Leia are twins put an end to any semblance of a relationship, and Leia married Han Solo.
Dani was a Zeltron, a race of human-like, pink-skinned aliens with empathic abilities and a culture which placed high value on sexual pleasure. A smuggler by trade, she first appeared in Marvel Star Wars #70, when Luke, Leia, and Han encountered her on the planet Stenos.
Dani became attracted to Luke as soon as she met him, and later proclaimed her love for him. Her affection seemed to make Luke feel awkward and embarrassed, and it's unclear whether he returned her feelings. Dani later joined the Rebel Alliance and began a relationship with a Chuhkyvi named Kiro.
Shira Brie was an Imperial spy who infiltrated the Rebel Alliance as a pilot in Marvel Star Wars #56. Soon after she and Luke initiated a romantic relationship, however, he shot her down in a battle when he lost his targeting computer and had to rely on the Force to sense enemy ships. He cleared his name after uncovering her real mission.
Shira didn't die as originally believed, but needed many cybernetic body parts in order to survive. After being trained by Darth Vader himself, she returned as the Sith Lady Lumiya. Many years later, she returned in Legacy of the Force to train Jacen Solo, Han and Leia's son, as a Sith Lord. Her final revenge against Luke was letting him kill her in a duel, bringing him perilously close to the dark side.
Tanith Shire first appeared in Darth Vader Strikes, a comic strip by Archie Goodwin and Al Williamson. Enslaved by the Serpent Masters, she encountered Luke while he was on a Rebel spy mission and was immediately attracted to him. After Tanith helped Luke escape an Imperial trap, he defeated the Serpent Masters and freed all their slaves. Due to Luke's responsibility to the Rebellion, however, Tanith decided not to pursue a relationship with him.
In The Paradise Detour, another comic strip by Goodwin and Williamson, a Mind-witch named S'ybll takes Tanith's form in order to seduce Luke. He realized that she just needed his life force to fuel her powers, however, and left her.
Alexandra Winger was a Force-sensitive pilot who appeared in several short stories in the magazine Star Wars Adventure Journal. The Force gave her several prophetic dreams, including visions of herself with Luke Skywalker -- although, at the time, she didn't realize who he was. When they finally met on a mission for the New Republic, they shared a kiss, but they parted ways and the relationship never progressed.
First appearing in The Truce at Bakura by Kathy Tyers, Gaeriel Captison was a senator of Bakura. She met Luke Skywalker when the Rebel Alliance offered aid to Bakura during the Ssi-ruuvi invasion. Although she and Luke expressed their mutual attraction, she was hesitant to act on it because of her religious beliefs: according to the religion of the Cosmic Balance, Jedi disrupted the balance of the universe by grabbing too much power for themselves.
Ultimately, Gaeriel rejected Luke and married a Bakuran, Pter Thanas. They met again in the Corellian Trilogy by Roger MacBride Allen, and Luke provided for Gaeriel's daughter after her death.
Mary was a resistance leader on the planet Solay, whom Luke met in Marvel Star Wars #89. After the Rebels helped overthrow the corrupt government on her planet, Luke and Mary fell in love. This was one of Luke's more serious relationships; he even considered leaving the Rebel Alliance to help Mary rebuild her planet. Mary was killed during an Imperial invasion, however, leading Luke to touch the dark side temporarily in his grief.
Teneniel Djo was a Force Witch, part of a matriarchal tribe of Force users on the planet Dathomir. In the novel The Courtship of Princess Leia by Dave Wolverton, Han Solo wins Dathomir in a card game and brings Leia there to prevent her from marrying Prince Isolder of Hapes.
Luke and Isolder chased after Han and Teneniel Djo captured them, intending to make them her husbands. She was initially attracted to Luke, amazed by his ability to use the Force as (she believed) only a woman of her tribe could. She later married Isolder, however, and became the Queen Mother of Hapes.
Jem was an Ysanna, a member of a Force-sensitive tribe of Humans on the planet Ossus. In Dark Empire II, Luke encountered Jem when he and Kam Solusar were searching for ancient Jedi knowledge on Ossus. The daughter of her tribe's shaman and chief, Jem became Luke's guide. He began training her as a Jedi, and they soon began a romantic relationship.
Their time together was short-lived, however; Jem died while trying to save Luke from Dark Jedi on New Alderaan.
Formerly known as Callista Masana, Callista Ming was a Jedi of the Old Republic. She survived Order 66 and, although she died soon after, was able to use the Force to project her essence into a ship's computer. Luke Skywalker encountered her 30 years later in the novel Children of the Jedi by Barbara Hambly; despite her lack of a body, the two soon fell in love.
When Luke's Jedi student Cray Mingla wished to die and join her lover, Callista was able to transfer her spirit into Cray's body. As a result of the transfer, however, Callista became unable to touch the light side of the Force. Luke tried to help retrain her and maintain their relationship, but she realized that they couldn't work out and left him.
Akanah Norand was a Fallanassi, an order of Force-sensitives who referred to the Force as the White Current. She first met Luke in the Black Fleet Crisis by Michael P. Kube-McDowell, claiming that his mother was a Fallanassi teacher. Wanting to learn more about his family's history, Luke followed Akanah around the galaxy.
Although they became romantically involved, their relationship fell apart once Luke learned that Akanah had lied to him. She knew nothing about his mother, and was only using him to help track down her people. Years later, Akanah helped train Jacen Solo in different philosophies of the Force.
Mara Jade was an Emperor's Hand, a Force-sensitive trained by and loyal to Emperor Palpatine, and later the member of a smuggling organization under Talon Karrde. She met Luke Skywalker in The Thrawn Trilogy by Timothy Zahn, when she vowed to kill him to avenge Palpatine. Their common enemies, however, drove Mara and Luke into an uneasy alliance.
Mara gave up the Dark Side and became a Jedi, training under Kyle Katarn. Although she and Luke crossed paths several times, they did not realize their attraction to each other for another ten years, during the Hand of Thrawn Duology by Timothy Zahn. They married (in the comic Union) and had a son, Ben. Mara's death in 40 ABY devastated Luke, sending him on another brush with the dark side.