This question has been asked many times… As usual the best (and longest!) answer comes from Diana herself.
“Q: Several of us read and reread the books, discussing them and trying to figure out why Claire and Jamie did what they did or reacted the way they did. We all have one question, though: Why was it so important to Claire to take back Frank’s wedding ring at the end of Drums? None of us would have taken it back! Can you explain what your thinking was on this point? Even given Claire’s history with Frank, her love for Jamie was so great, why would she feel the need to have any ring other than his?”
“A: I’m tempted to say that this is one of those things that you either see or you don’t see—but I’ll try to explain. Yes, Claire has history with Frank—a lot of history, and very mixed, in terms of joy and pain. He was her first love, her first husband, and when she married him, she did so with the full intention of being married to him for life. She is, after all, a very loyal and honest person. For her to have “left” him and chosen to stay with Jamie was an act of betrayal, and she knows it. Frank did nothing wrong; his only “crime” was not to be Jamie. You figure it’s fine to forswear your vows and run off with somebody else, just because they’re more attractive than the person you married? Claire doesn’t.
Granted, the circumstances were extremely pressing, and she had overwhelming reasons—emotional as well as physical—to do what she did, but it was betrayal, and the knowledge of it nags at her now and then through the two early books (remember her dreaming of Frank and the miniature portraits?). “Her feelings of guilt and her loyalty to Frank are what cause her to press Jamie not to kill Jack Randall, in order to save Frank’s life.
Later, when she goes back, pregnant and emotionally shattered, it’s Frank who picks up the pieces and glues their life back together. He accepts Brianna fully as his own—which is not something that every man could do; he supports Claire in her decision to become a doctor, appreciating (even as he envies) her sense of destiny. This is pretty much the admirable behavior of an honorable man, and Claire both knows and appreciates it.
Now, in terms of their personal and sexual relationship… she abandoned him, and came back only by necessity, carrying the child of a man with whom she obviously remains in love. You figure this was easy for Frank to accept? He’s a man with a lot of compassion—but he’s very human. He makes repeated efforts at their marriage—and so does Claire—but the simmering rage at her betrayal is still there, underneath. Since he can’t or won’t admit the truth of her story, they can never discuss it fully, never resolve the situation; “Jamie Fraser is always the ghost that haunts their marriage. Small wonder if Frank takes lovers now and then—as either revenge, or simply as refuge.
Okay. So this is a difficult, complex relationship. The difficulties and guilts don’t mean that there is nothing of value between them. The love they once had for each other is still there, augmented and supported by their united feelings for Brianna, diminished and eroded by the memory of their betrayals of each other—but still a pillar, standing like a desert rock, twisted and shaped by wind and rain.
If Claire were capable of simply walking away from this sort of history and feeling, abandoning a huge piece of her life and identity, just because she was now in a different place… well, she wouldn’t be capable of loving Jamie in the whole-hearted way that she does. She wouldn’t be a whole person.”
“As it is, she’s now relieved of the guilt of her flawed relationship with Frank, and free to treasure the memory of its good moments. Jamie, being the whole-hearted person he is, is aware of this, and wants her to know that he’s able to accept the knowledge of what she shared with another man—the one thing Frank couldn’t do. This has something to do with the nature of love and the concept of obligation as part of love. While Roger is contemplating the issue explicitly “Love? Obligation? How the hell could you have love without obligation?” he wondered), Jamie and Claire are living it implicitly.
For her to refuse Frank’s ring, and essentially reject all he was, to deny the value of thirty years of a complex but valuable relationship—well, that would be both dishonest and petty. And neither Claire nor Jamie is small in mind or heart.”