My Husband's Mistress Is My Stepsister

Isabella's POV

The last therapy session of the day ended at 4:30 PM, thirty minutes earlier than usual. I had deliberately cleared my schedule, something I hadn't done in three years of marriage. Valentine's Day. The thought felt foreign on my tongue, like speaking a language I'd forgotten how to use.

I slid into my car and pulled out of the parking garage beneath my practice. The February afternoon sun cast long shadows across Palo Alto's manicured streets, and for once, I wasn't thinking about my patients' breakthrough moments or treatment plans. Instead, I was rehearsing words I'd never said before.

'Maybe Damian was right. Maybe I should try harder to feel... to love.'

The grocery store bag in my passenger seat contained wagyu beef and ingredients for homemade chocolate truffles. I'd even bought candles, though the gesture felt as clinical as prescribing medication. Still, I was trying. After three years of him complaining about my emotional unavailability, I was finally making an effort.

The drive home took twelve minutes. But today, something was different. As I turned into our driveway, a splash of pink caught my eye.

A pink sports car sat in front of our house.

Selena's car. My stepsister's car.

My hands tightened on the steering wheel. What was she doing here?

I parked in the garage and gathered my things, that familiar analytical calm settling over me. There had to be a logical explanation. Maybe she was dropping something off. Maybe she needed money. Selena always needed money, despite the trust fund and her influencer income.

The house was quiet when I entered through the side door, my heels clicking against the marble floor. Too quiet. Selena's designer bag lay discarded on our white leather sofa, and Damian's blazer hung over the back of a chair.

The air smelled wrong. Not the usual blend of my candles and Damian's cologne. This was something sweeter, more cloying. Selena's signature perfume.

Then I heard it.

Soft sounds drifting from upstairs. A giggle I recognized too well, followed by Selena's trademark breathy voice: "Oh, daddy..."

My shopping bag hit the floor with a soft thud, organic vegetables spilling across the pristine marble.

I slipped off my heels and climbed the stairs barefoot, each step silent. The master bedroom door stood slightly ajar, and through the gap, I could see everything.

Damian and Selena, tangled together on our bed. Our bed. The cotton sheets I'd picked out, the mattress we'd christened on our wedding night. She was straddling him, her bleached blonde hair cascading over her bare shoulders, and he was looking at her with an expression I'd never seen before.

Wonder. Desire. The kind of raw want he claimed I was incapable of inspiring.

I should have felt devastated. Heartbroken. Instead, I felt... curious. Like I was observing a case study.

"Isabella?!"

Damian's voice cracked like a teenager's. He'd spotted me in the doorway, and his face went white beneath his carefully maintained tan.

I leaned against the doorframe, crossing my arms. "I finished work early. Thought I'd surprise you for Valentine's Day."

Selena scrambled to cover herself with the silk throw blanket. Her face was flushed, whether from embarrassment or exertion, I couldn't tell.

"Sis, we can explain..."

"No need." I kept my voice level, professional. "I can see exactly what's happening."

Selena's shock melted into something uglier. That familiar smirk she'd worn since she was fifteen and discovered that batting her eyelashes at daddy got her whatever she wanted.

"Actually, Isabella, maybe this is for the best. Now we can all be honest." She made no move to leave the bed, apparently comfortable discussing this while naked. "Damian deserves a real woman, not some ice queen who treats him like one of her patients."

I turned and walked to our walk-in closet, pulling out one of Damian's suitcases. I began folding his clothes with mechanical precision.

"What are you doing?" Damian scrambled into his boxers, finally showing some sense of urgency.

"Packing your things."

"Isabella, stop. Let me explain..."

I held up a hand. "Explain what, exactly? Market research? A clinical trial on the effectiveness of sleeping with your wife's family members?"

Selena laughed. That tinkling sound she'd perfected for her social media videos. "See? This is exactly what I mean. Even now, you're being clinical. You don't feel anything, do you?"

The words hit deeper than they should have. Because maybe she was right. Maybe I was exactly what Damian had always accused me of being: a beautiful, successful shell with nothing real inside.

"Get out," I said quietly.

"What?" Selena blinked those artificially enhanced lashes.

"I said get out. Now."

Damian stepped between us. "Isabella, be reasonable..."

"Reasonable?" The word came out sharper than intended. "You want me to be reasonable about finding my husband fucking my stepsister in our bed on Valentine's Day?"

Something in my voice made Selena finally reach for her clothes. But she couldn't help herself. Even pulling on her designer jeans, she had to have the last word.

"You know what your problem is, Isabella? You're frigid. You always have been. Damian told me how you just lie there like a dead fish. How you analyze everything instead of just feeling..."

The crystal vase on my nightstand shattered against the wall before I'd consciously decided to throw it. Selena shrieked, covering her head as glass rained down around us.

The mirror above our dresser was next. Then the framed photo of our wedding day. Then Damian's collection of vintage whiskey.

"Jesus Christ, Isabella, stop!" Damian grabbed my wrist as I reached for another target.

I yanked free and turned to face him. Really face him, for the first time in months. His carefully styled hair was disheveled, his face flushed with panic and something that might have been shame.

"You're scaring her," he said, as if that mattered more than anything else in this moment.

Selena had finished dressing and was backing toward the door, her phone clutched in her manicured hands. Probably already composing the social media story about her psycho stepsister.

"Damian, I'm leaving. This crazy bitch is dangerous."

He looked between us, and I saw him make his choice. He moved toward her, protective, concerned. Not toward his wife of three years, but toward the 25-year-old with daddy issues and a social media empire built on bikini photos.

"I'll call you later," he murmured to her.

After she left, the house felt different. Charged. Like the air before a thunderstorm.

"Are you satisfied?" Damian asked. "You terrified her."

"Should I apologize? For having a reaction to finding you cheating in our home?"

"This is exactly the problem!" His voice rose. "You're cold, Isabella. Even when you're angry, you're calculating. Living with you is like living with a computer."

I started gathering the broken glass, my movements careful and controlled. "So this is my fault."

"You want to know why I need Selena? Because she makes me feel desired. Wanted. Not analyzed and treated like one of your broken patients."

I straightened slowly, a shard of crystal cutting into my palm. Blood welled up, bright red against my pale skin.

"So this is my fault," I repeated.

"You're just like your mother. Never able to keep a man's heart! She couldn't keep your father, and you can't keep me. Being cold is just a genetic disease in your family!"

The slap echoed through the room. My palm, still bleeding from the glass, left a crimson mark across his cheek.

"Get out." My voice was deadly quiet. "Take your things and get out of my house."

He left. They both left.

And I was alone with the wreckage of my marriage and the ghosts of memories I'd spent twenty-two years trying to forget.

The house settled into silence around midnight. I sat in our destroyed bedroom, moonlight filtering through the broken mirror and casting fractured reflections across the walls.

Damian's words circled in my head. Mom had been gentle, so gentle. Even when dad brought Camila home, even when she'd been replaced by a woman ten years younger, Mom never screamed or threw things or fought back. She just... disappeared. First her smile, then her voice, then everything else.

I was ten when I found her in the bathtub. The water had been cold by then, tinged pink from the precise cuts on her wrists. Her eyes were open but empty, staring at something I couldn't see. Maybe Damian was right. Maybe I was destined to be unlovable, just like her.

I walked to the ensuite bathroom, avoiding my reflection in the mirror above the vanity. In the bottom drawer, beneath spare towels and sample-sized luxury products, I found what I was looking for.

A surgical scalpel. I'd kept it from medical school, sometimes used it in lectures about self-harm to show my patients the reality of what their tools could do.

The blade caught the moonlight as I turned it in my hand. Such a small thing to hold so much potential for ending pain.

I pressed the edge against my wrist, feeling the cold metal bite into my skin.