Looking back on it, the crucial moment occurred when she noticed she was still wearing underwear.
Normally that would have been a good thing -- modest and prudent. She wasn't the type to 'go commando', especially in a sun dress. But the beach trips with her sister and brother in law had developed their own rituals, and changing into her bathing suit at the beach was one of them. After the first time, when she had been caught unprepared for the decision to actually go swimming (the surf was high and it was almost sundown), she had been more careful. On that occasion, she had been wearing bulky shorts and a flimsy t-shirt. She decided to wear the shorts into the water, but she didn't want to go home in wet panties, so she slipped them off, sitting on the cool sand, and then struggled back into her shorts. She had stood on her knees to wiggle into the shorts, naked from the waist down for a few seconds. The question was: had David glanced over at her during that unguarded moment? He could have seen everything -- or did the sightlines limit him to a view of her bare ass? She would normally have said bottom, or tush or even backside... but something in the way David had been looking at her lately, even fully dressed, made the raw single syllable more appropriate.
Bigger question: did she want him to have seen her? She certainly didn't care any more if Sam looked at her, and she was supposed to be in love with Sam.
More troubling still: the night after that beach day she climbed on top of Sam and really made love to him for the first time in... well, a long time. Too long. So Sam was happy. And so was David: he had certainly been staring at her after that swim, when she bobbed out of the water with her soaked flimsy t-shirt clinging to her breasts, as close to naked as he'd ever seen her, stiff nipples showing pink through the pale membrane of cotton.
Funny, she had caught Sam glancing at her in that shirt a few weeks before -- it was a little immodest even when it was dry -- and said something like "I'm never wearing this shirt in public again." Well, so much for that resolve. She hadn't just worn it, she had sat on the beach a foot away from her extraordinary brother in law, damp and brazen, and let him stare. Carol acted as though it meant nothing. Maybe it did mean nothing. Beach rules were different. You were supposed to show a little skin there. Anyway, David and Carol's marriage was strong, supernaturally strong, or so it had always seemed. A moment of permissible summertime indecent exposure couldn't change that.
She had worn the wet shorts home, and the next time she wore bikini bottoms under them. Still, she had to change into the top on the beach. She would have called it another oversight, then; now she knew better. She had stood a little apart, facing away, while David turned and Carol made a note in the margins of her book, and bared her back to him. But she had left her top on the sand and she had to lean down sideways to pick up the scrap of fabric. David's could see everything. She could feel his eyes on her, memorizing the slight droop of her small firm breasts.
Their eyes met and he didn't look away.
That was the sexiest thing of all: that he didn't look away.
It felt strange and spooky and ambivalent. She didn't want to cheat on Sam; she certainly didn't want to seduce her sister's husband.
But here she was, on the way to yet another beach afternoon, with her bathing suit in her big straw purse, along with the sun screen and bug spray and other practical supplies, wearing her sexiest panties, knowing she would have to slip out of them at some point, or go swimming with them on. She could have pulled over and changed; or just put her suit on in the bathroom at the cottage. But she didn't want to. Her psychiatrist had said, "Find the thing that excites you, and then do It," when she complained about her dormant libido.
