This is anime. They showed this arc in the anime. Hehe you're right. Kenshin is a widower. I watched the whole Rurouni Kenshin Arc including every OVA and movie. Here's the story:
[SPOIL]At the beginning of the story, we see a young boy named Shinta and his "family" get slaughtered by wandering bandits. Fortunately Shinta survives because the legendary master of Hiten Mitsurugi, Hiko Seijuro saves him in time.
Hiko gives Shinta his new name: Kenshin Himura, because he believes Shinta in not a name fit for a warrior. Kenshin spent his days training and mastering his craft: the Hiten Mitsurugi style.
Living in the Meiji Era opened Kenshin's eyes about life. About the pain and suffering the war is dealing to innocent people. So, even against Hiko's wishes, Kenshin joined a band of men dedicated to keep peace in Kyoto, by killing high ranking Government officials who kill and plunder innocent citizens.
During a mission instructed upon him by his chief officer, Kenshin killed a government official, who was unjustly identified by the group, saying that the man was evil and unjust to be a ruler, but the man was really kind and compassionate. Kenshin quickly killed the man, however he had a very hard time against one of the man's bodyguards. A man named Kenta. While battling this man, Kenshin received a scar on his face, a line that symbolizes the man's hatred for Battousai, because after the said mission, Kenta was going to marry his beloved.
Kenshin's ranks inside the group quickly rised, and one day, while walking after a meal, he encountered several members of the SHinsengumi. There he killed them in such a brutal fashion, that the area was engulfed in a rain of blood. After killing them, Kenshin was surprised to see a woman, wearing a white kimono, her face wet with blood. She faints in front of the surprised Battousai.
Kenshin, known as Battousai was thought to be heartless, that is why everyone was surprised when he brought the woman to his hotel, cared for her and nursed her back to health. Kenshin, since the day his family died, for the first time showed love and compassion towards another. The woman grew healthy and she eventually grew fond of Kenshin.
One day, when Kenshin and the woman he saved, whose name was Tomoe, received a report that a neighboring rival was searching for Battousai.. They wanted to Kill Kenshin. Kenshin's group decided that they must protect their number 1 slasher. That is why they decided to send Kenshin up a mountain to hide, Tomoe with him to protect him. They pretended to be newly weds to escape suspicion.
One day Tomoe received a visit from her younger brother Enishi. According to Enishi, Tomoe was the only person that loved him, she was everything to Enishi. And he refused to let a "murderer" live with his sister. Tomoe hushed her brother and finally admitting that she loved Kenshin. Enishi feeling defeated quickly left, a slight smile in his face. That night, Kenshin and Tomoe sealed their love by making love next to a fireplace.
When dawn broke, Tomoe left their cottage saying the words: "You killed my first love. But you, my second love. I will not allow you to die!" Tomoe was Kenta's fiancee!
It turns out that Tomoe was initially a spy sent by Kenshin's rival, to seduce Kenshin and discover his weakness. However, Tomoe fell in love with Kenshin. When Tomoe reached their hideout, she lied to the group's leader, saying that Kenshin is most vulnerable in his sleep.
The leader, angry, beat and raped Tomoe. He then sent several henchman to dispose of Battosai. Enishi watching on, angry at the leader, took out a dagger and tried to stab him, however, Tomoe told him to flee. Enishi escaped.
Once Kenshin discovers his love's departure, he went to look for her. On his way to find Tomoe, he faced sevearl opponents, and, at one point, lost his vision because of a bomb exploding in front of him.
At last Kenshin reached the hideout, and proceeded to fight the boss. However because Kenshin was temporarily blinded, he proved no match. At last the boss, was ready to deliver his final blow, Kenshin straightening his sword plunged directly towards his enemy, ready to stab the man who defiled his beloved. Tomoe realized that Kenshin might kill his opponent, but he will also be killed in the process because of his opponent's next blow. She decided to stand in front of the two men, just before the blade stabbed Kenshin. But in the process Kenshin accidentally stabbed Tomoe, the blade piercing her flesh, and ultimately, stabs his opponent as well. Because Tomoe shielded Kenshin, Kenshin was not killed. As Tomoe cried, and right before she died, she muttered the words: "I love you...." She then used her dagger to slash Kenshin across the face foming Kenshin's X-shaped scar---symbolizing his sins.
Enishi, witnessing the event came upon the conclusion that Kenshin killed Tomoe purposely, just like what he did to Kenta. He decided that the only way that he could be truly happy, was to kill the man who took everything away from him: His brother in law, Kenshin Himura. [/SPOIL]
The story is then continued towards the Jinchuu arc, in which Kenshin battles Enishi. Wanna know the story? Just PM me and I'll be glad to tell you!
Just a spoiler: [SPOIL]Kenshin and Kaoru has a baby, his name is Shinta, the boy carrying Kenshin's strenghth and innocence. Kenshin dies in the end.[/SPOIL]