John & Marlena
John and Marlena's love affair began in 1986 when Dr. Marlena Evans met a John Black at the hospital.  They became friends, and after discovering that he had amnesia, she helped him recover his memory through hypnosis.  She was shocked to discover that he was her supposedly dead husband Roman, and they renewed their vows.  The next year, Marlena was presumed dead in a plane crash.  Four years later, Roman saw his wife on the docks- it turned out that she'd been held captive on an island.  it was discovered that Roman was really Roman- the real Roman had been in a jungle prison.  John Black turned out to have been brainwashed.
John married Isabella, who had Brady, but she died of cancer.  John and Marlena realized later that they still had unresolved feelings for each other, but could do nothing about them because Marlena was married to Roman.  By 1993, they couldn't restain themselves any longer and made love on a desk in a conference room at Titan.  Belle was conceived as a result of that, and when she was born, everyone beleived that she was Roman's(except Sami and Stefano).  John began seeing Kristen.  While Belle was beeing baptized, Stefano forced Marlena to reveal her affair with John.   Roman divorced her, and Stefano lured John and Marlena to Maison Blanche, and John discovered that he was a priest.
In 1995, Marlena became possessed by the devil, and John had to perform an exorcism to save her soul.  He was released from his vows, and hooked back up with Kristen, even though he was still in love with Marlena. 
John was framed for Tony's murder in Aremid, and while on death row, wrote a love letter to Marlena.  John was cleared at the last moment, and Kristen hid the letter from Marlena.  Marlena found the letter eventually, and knew about Kristen's deception, but kept quiet about it because Kristen was pregnant.  Stefano kidnapped Marlena, and John rescudeed her in Paris.  Kristen lost the baby, but hid it from John by wearing a pad over her belly, so that John would stay with her.  Stefano hired a pregnant woman, Susan, who looked exactly like Kristen, to help.  In 1997, Kristen(Susan) gave birth to John Jr.  Kristen locked Marlena in a secret room in the wine cellar to keep her from revealing the sceme to John.  Then, Susan turned on kristen and locked her in the room with Marlena.  When Susan finally confessed, they were released. 
John and Marlena were back together again, and were almost married until Kristen brought back Roman, who had been thought dead.  Roman tried to win back Marlena, but he wasn't successful, and she remained with John.  John and Marlena were married in July 1999, but John's search for his past, and Gina's obssession with him threatened to keep them apart.  Now that Gina is dead, John can move on with his life, especially since he now knows that he did not father Hope's baby.  John and Marlena can now focus more on their family, but the mystery surrounding the Dimeras continues to keep them busy.  The recent Salem Stalker mystery and Marlena's "death" once again threaten to divide this couple.