Disclaimer: I don't claim any rights to Inception, all Chris Nolan's =)
Ariadne always liked to consider all things (situations, choices, places) equally. Her mom was a lawyer and her dad a chemist so facts and unbiased observations (never opinions those were biased) were only considered in their household. So when her parents divorced just before she graduated (neither showed by the way, she had to get a ride home with a friend), Ariadne decided to live with neither and go to Paris. She had just turned eighteen, so Ariadne was free to go as she pleased. Ariadne was glad for the scholarship she had, because neither parent was willing to help financially (it wasn't like they were poor, rejection was a hard pill to swallow).
Therefore, if she were asked whom she loved more, she could reply neither. Ariadne disliked both of them equally.
In beginning of her first year of college, Ariadne had two roommates who were opposites. One liked to party, skip classes, and perpetually complain. The other liked to read, had perfect attendance, and stewed quietly on her grievances. She couldn't say whether she preferred one over the other (even though most would assume the quiet one was the better option). Party girl Irina, although as deep as a puddle was incredibly nice and Quiet Serena (Ariadne thought it ironic their names rhymed) was timid and awkward at times. Nevertheless, she loved them both equally, because Irina gave her a social life and Serena made her studious (the tension between them was thick though, waiting for the scales to tip).
In the end of her first year of college, Ariadne had applied for a single room.
When Ariadne met Cobb, went into his dreams and thrust out of his dreams. She was curious about Mal, wanted to know who she was and what she was. Arthur (whom she decided was quite interesting and quite handsome) helped to fill in the void of unknowns on the mysterious Mal. She wanted to help Cobb, felt bad for Cobb; after all, the Mal she knew was all jagged edges and coiled tension.
But, when she washed up onto the shore of limbo, where buildings crumbled and the city resembled a glorified grave, she felt equally bad for Mal. In that lonely suite, that once resembled a home Ariadne learned that Cobb first performed inception on his wife (his other half, his lover) that things came to a standstill for her.
When Ariadne fell those thousands of feet into the waters below she didn't know what to feel about both Cobb and Mal. She only knew that she couldn't side with either, despite how much Ariadne liked Cobb, she understood Mal too (the descent made more sense now).
Two weeks after the Fischer job, she had gotten calls from both Arthur and Eames (they liked her work, would she work for…). Ariadne told them, that she would be interested to work, but only together. She liked Arthur's quiet dedication to his work, and Eames' charming personality (not to mention they were both extremely handsome).
It worked out in the end anyways; they worked beautifully together (despite the occasional squabbles between Arthur and Eames).
After months of working together, Arthur finally broke his façade of posh veneer and quiet patience (too many moments of caught gazes across the room and accidental brushes of skin against skin that drove him mad with longing). His dark eyes on her face and his hands (Ariadne would describe them deceptively strong, perfectly Arthur) on her slender shoulders. "I love you Ariadne." His face twisted, from tense to forced blankness. "I'm not crazy about it. But I would prefer you felt the same."
It was typically Arthur to say something that intense, and follow it up with his dry sarcasm, Ariadne mused. Before taking his face (she found it cute he was so intensely serious, only Arthur) and fusing their lips together in a kiss. When they parted (with flushed faces and bruised lips) Ariadne gave him a quick peck (he was too cute sometimes) and told him she loved him too. She smiled as his relieved expression (an expression unnecessary, she was his long ago if Arthur had realized it sooner).
Most would say that Ariadne preferred to stay neutral on most things and it was true to some degree. However, Ariadne would differ when it came to Arthur because there was no comparison and no other half (but she would consider herself that now). If Ariadne was asked whom she loved more, was attracted to more, favored more—there was no equal in her eyes (no doubt to the depth of her feelings), there was only Arthur.