Luckily, she has
Did you guess Lord John Grey? Because yes, Claire and Lord John end up married in book seven, and yes, they drunkenly (and full of grief for the loss of Jamie, whom they both love with all of their heart) consummate that marriage.
While on a second honeymoon in Scotland with her husband, Frank Randall, Claire inadvertently travels two hundred years into the past, where she meets and eventually marries Jamie Fraser.
As ambitious and enormous as the world of Outlander is, it's the characters and their relationships that make the story so compelling. At its heart is the love shared between Claire and Jamie, two people who ultimately would not let time or distance—even hundreds of years—keep them apart.
So, technically, Claire has three husbands in the Outlander books.
“He's about 25,” Gabaldon said. It's an interesting response. If you're up to date on the series, then you know that Jamie is not dead at the age of 25.
During An Echo in the Bone/Written in My Own Heart's Blood, Claire marries for the third time. This time it's to Lord John Grey.
When Jamie goes to jail for illegally dueling Black Jack Randall in Paris, he's imprisoned in the Bastille. Claire, who miscarried their daughter Faith, goes to meet the king and plead for him to free Jamie so they can return to Scotland.
Jamie: "Claire, it was you. It's always been you, and it always will be. Get into bed and put the candle out.
Jamie did remain faithful to Claire. It didn't stop him from being aroused. However, it just made him miss and want Claire more. Even in their 50s, the two are ready to be with each other sexually.
Claire realises that she had fled because she was afraid that Jamie wouldn't choose her, but she now knows that her future is with Jamie and she will stay.
The answer is simply no. Claire and Jamie did not have any children after Brianna. Claire, who was pregnant with Brianna at the end of the second part/book, traveled through the stones and spent 20 years in the 20th century with Frank, but they did not have any children together.
Therefore, she kept it a secret in order to protect Jamie's feelings. Though Claire was able to forgive Jamie for his infidelity with Laoghaire in the past, she was also aware that the situation was different in this case, as she was the one who had committed the unfaithful act.
Grey falls in love with Jamie, who rejects his advances. Still, Grey cannot dismiss his feelings.
Claire chooses Frank for 20 years until his death and then she finds out Jamie survived Culloden. She heads back to the past to choose Jamie for a second time. There's no way Claire and Jamie will choose someone other than themselves after this. They are endgame, and it doesn't matter what anyone else thinks.
It's all pretty bizarre, but Brianna sensibly plays along to save herself, and even convinces Bonnet to let her go home and get Jemmy. Well, at least until Bonnet wants to seal their agreement with a kiss, at which point he realizes Brianna has no real feelings for him.
Jamie decides that he can forgive her. He can move on from it. However, he makes it clear that she is to never sleep with another man again.
In September 1764, Lord John told Jamie he intended to marry Isobel Dunsany and become William's stepfather. Jamie offered his body to Lord John, who declined. Jamie kissed him.
Jamie also has two stepdaughters, Marsali MacKimmie Fraser and Joan MacKimmie, from his marriage to his second wife, Laoghaire MacKenzie.
Claire asks Lord John if he believes she (and Brianna and Roger) are from the future, to which he says that he doesn't, but that he will behave for all appearances as though he does.
1701-1800. Jamie and Claire have been separated for 20 years. He is hiding near Lallybroch after surviving the Battle of Culloden. Jamie is blackmailed into sleeping with Ellesmere's young fiancée Geneva and impregnates her.
Jamie's Secret is a story about a nine-year-old who loves soccer, playing with her best friend Sadie, and collecting crystals. She loves hugging and climbing trees, watching butterflies, and soaring on her swing. Jamie loves life and everything that points to it.
Later, after Claire has returned to the Ridge, she is confessor to Allan Christie, who explains that he was the one that fathered Malva's child, and then murdered her.
To recap: By Gabaldon's timeline, Jamie and Claire's age difference is 5.5 years, while on the show, that age gap shrinks to 4.5 years.