Penny Guisinger’s delightful “Shift: A Memoir of Identity and Other Illusions” returns more than once to the image of a Mobius strip. A one-sided surface in the shape of an infinite loop, the Mobius strip is both simple and profound (it’s worth a quick internet search to learn how to make one by twisting a strip of paper). In “Shift,” it serves as a symbol of a life, traversing terrain that is at once mysterious, mundane and transformative.

In its broadest outlines, Guisinger’s memoir is focused on one specific shift: in her late 30s she falls in love with her friend, Kara, and leaves behind her husband and straight identity. Guisinger’s short chapters unfold swiftly, in vivid bursts of detail and association. Reading them evokes the experience of meeting a new friend for coffee and hearing intriguing nuggets about her life and preoccupations: episodic, but not linear; quick, but not superficial. Her voice is searching, forthright and witty:

“Shift: A Memoir of Identity and Other Illusions,” by Penny Guisinger. University of Nebraska Press, $22.95

“Imagine that you are a thirty-eight-year-old woman and the primary breadwinner in your house. You are the mom of two kids, ages three and one. … Your marriage is a rickety house built on spindly stilts straddling a fault line in an earthquake hazard zone, so sometimes you think you might be working for FEMA, but you’re not issued a hardhat… You are sure you ordered the everything bagel of feminism topped with career fulfillment, skillful attachment parenting, a kitchen filled with organic whole foods, ample free time, and a vibrant social life. You are certain that if you’re not having it all it’s because someone’s doing something wrong.”

Guisinger takes us through discrete moments: from teenage experimentation, to visiting Provincetown with the boyfriend who would become her husband, to making music with the woman who will change her world, to struggling to parent well through divorce. She discloses problems with alcohol use and eventual recovery, though does not delve deeply into that aspect of her life — an omission that’s intentional if a bit unsatisfying. Ruminations about music, mathematics, science, abstract painting and more spark connections between the mysteries of the larger world and the mysteries of the human heart.

At its core, this book is concerned with something both singular and universal: It’s a love story. Anyone who has ever been poleaxed by love, awakening to an understanding that life will never be the same, will recognize the blend of euphoria and disquiet here. Meeting through friends, becoming colleagues in music and at work, the two women fall in love slowly and then all at once. On the precipice of a conversation that will finally reveal their feelings, Guisinger fiddles with the label on a beer bottle:

“I kept my fingers busy peeling shiny gold paper from the bottle, grateful for the darkness that separated us… There was a long pause. Fireflies, held aloft by invisible, membranous wings, blinked in and out of visibility. We both intently watched the darkness. Ahead, the tree line existed only as a dark shape yielding abruptly to stars.”

Later, Guisinger has a funny riff about how coming out is like using an old-fashioned paper roadmap: “It’s awkward and full of creases, and once you get the thing unfolded, you’ll never get it back in the glove compartment.” But the process of dissolving a marriage is serious business, especially when children are involved.

Guisinger and her ex-husband make valiant efforts to protect their kids from upheaval, including continuing to share a house together for a time. How they work it out, as co-parents and friends, is bumpy. Guisinger takes care not to gloss over the difficulties – which makes her family’s evolution even more affecting. She recounts turning to parenting books for guidance and finding them woefully insufficient:

“‘This isn’t as easy as your book made it sound,’ I imagined typing to the smug writer. ‘My kids are probably going to be fine, but the effort might kill me. Why didn’t you write about that?’”

Marching with her family in a gay pride parade in her rural Maine town – not out of any love for parades, but because she feels obligated to represent – she notes which of her neighbors are clapping on the sidewalk and which are scowling. Just after the parade, they head to a fast-food restaurant: “Our rainbow gear – flags, snap bracelets, flowery leis – was all stowed in the back of the car. In regular, rainbow-free clothing, we were covert again.”

These moments of visibility and retreat, of joy and jitteriness, are noteworthy to Guisinger because of how starkly they differ from the ease and freedoms of her straight married life. The shock of being the same person, but with different strategies for being public with her spouse, creates a dissonance that Guisinger examines with incisive clarity.

Guisinger and her wife marry in 2011, in Massachusetts, but they are not legally married when they drive home to Maine. That will change. Guisinger charts the whiplash-inducing, win-some-lose-some back and forth of having marriage rights rise and fall at the whims of the state legislature, the ballot and the courts. Of being in the grip of forces that feel both ruthlessly administrative and painfully personal:

“… with this marriage, I not only came full circle, but I also squared the circle, an idiom that means to do the impossible. Achieving same sex marriage rights in Trump country could be seen as an example of squaring the circle. Likewise, so could exiting my identity only to find that my new identity was barely even a shade different. I had walked the Mobius strip and come back queer.”

And now we come to our present moment, with new whims in play. Who’s to say how these rights may shift again. Queer people and families are likely to feel cold winds, in ways both predictable and unpredictable. Anyone who thinks the conservative majority on the Supreme Court would not be open to weakening or dismantling federal marriage equality hasn’t been paying attention. The support of allies clapping at pride parades everywhere remains essential.

One hat trick of good memoir writing is that, in presenting an intimately specific life story, readers find unexpected affinities and insights that resonate with their own experiences. That’s to say, “Shift” has something to offer to anyone who has ever realized, midway through the drive, that it’s time to scrap the roadmap. It’s for anyone who has ever taken stock of life’s twists and turns, marveling at how it’s possible to come so far and still be yourself. Reader, I suspect it may be for you.

Genanne Walsh is the author of a novel, “Twister,” and a creative nonfiction chapbook, “Eggs in Purgatory.” She lives in Portland.