It makes perfect sense. She created him, therefore the perfect specimen. Every inch of her son was molded and formed inside of her body as he fed on her for nine months during pregnancy. As an adult she was able to see how attractive he'd become and often found herself jealous of things like him dating or having girls over the house. She made it clear that she would be the only woman in his life and that a mother always comes first. 

As an only-child and having no father figure, he was clearly a momma's boy. She breastfed him way longer than she should have and found herself unable to "let go" of him as he became older and older. By the time he'd become legal, she was doing things like spanking him in the butt and moaning into his ear sexually, running her fingers through his hair, expressing how even though he's an adult now that he's still a "good boy". She knew every part of his body, and his cock was no exception. Her son had been sporting a very massive and impressive erection. Years of being curious about his adult cock made her pussy become so wet with excitement as she froze, stunned one morning watching him masterbate. Moaning "Mommy!" and making a huge mess.

He started becoming more and more dependent on his mother and they did everything together. Going to the gym and working out, she was constantly correcting him on his form, wearing tight yoga pants and focusing particularly on his cardio, occasionally bumping and rubbing into his penis by accident. He wore exactly what she told him to - extra tight workout pants which showed off his bulge. Every yoga class she dragged him to she made absolute sure that he had full view of her ass, asking him to hold her in position, her wet, sweaty pussy right in his face as mommy smells wafted into his nose causing his cock to shoot straight up. 

They did things like kissed on the lips in public, hugs that lasted extra long, dressed more revealing around the house, etc. This slow, drawn out, but incredibly hot process eventually led to a breaking point one day. The door slid open as she smiled at her son, hot steamy water dripping down his youthful, strong body. Naked as the day he was born, she stepped into the shower with him and began washing his cock, knelt down. She rubbed soap from his tip all the way to his large balls, slowly getting every single inch, then making her way to the crack of his ass. She watched his eyes widen as she teased his asshole with her finger and began kissing the tip of his cock. At almost breakneck speed he submitted to her as she kissed it more and more as the hot water rained down on both of their bodies. Precum began to form as he flinched and cooed at every sensation his birthgiver wanted him to experience. Being his mother, it only made sense for her to understand his cock more than he does. 

She asked him how much he loved her, how much he had grown, how proud of his penis she was, etc.

All he could mutter out while in complete ecstasy was "Yes, mommy..." as he literally panted for breath. 

She began jerking, kissing, and eventually sucking his momma-snake. He couldn't bear it anymore and exploded right then and there. Thick, warm ropes of baby batter began pumping out of his balls into her eager mouth. She couldn't believe how much her son came as she swallowed all of it, the thick goo sliding lovingly down her throat. They both expressed how much they loved each other and that he could always cum to mama.