Jessica pushes you head first into her vagina, feeling the first wave of pleasure hit. She pushes you in and out over and over again, rubs her breasts, and moans.
She's enjoying all of this, and although you don't get much from this, her pleasure is enough for you.
You feel her heart beating as she thrusts you in faster and faster, quickly climaxing. In a moment of pleasure, she accidently shoves you completely into her womb.

"Uh, Jessica?" You say. "I'm kind of stuck in here"
Jessica yawns. "I'm tired, I'm going to go to sleep"
"But what about me?"
"Can you breath in there?"
"Yeah, but-"
"Then you should be fine, I'll get you out tomorrow"
You pause for a moment. "Goodnight, Jessica"
"Goodnight, Jack" she says, before falling asleep.

You weren't at all tired before, but for some reason, you're beginning to feel sleepy. You begin to feel soothed, not noticing the liquid filling up her womb, nor the umbilical cord that's now connected to your belly. Your body begins to grow younger and younger. Undoing puberty, making you a child, then a toddler, then a baby. And soon, you become just a set of cells again. You take your spot inside the womb, and begin to grow into a new child.

A few hours later, Jessica wakes up.
"Good morning, Jack. Did you have a nice sleep?" She asks.
She then realizes something is off, and despite not being visible, she could somehow tell she was pregnant.
"Oh no... Jack?" She says, with no response.

Jessica being pregnant wasn't something she could hide, and because nobody would believe that you had been shrunken, she lied. She said that you got her pregnant before leaving town without saying where you were going. She didn't want it to be something so negative against you, but what choice did she have?
Although her parents found out and were furious, they were never home enough for that to matter. She kept the child, and despite her age, she was determined to be a better mother to her new daughter than her parents had been to her.
And while Jessica had always been independant, this was a different deal. She was worried she might fail, but your family helped. They knew that your dissapearance left her with nobody, so they decided to assist her, even taking her in when she got kicked out. Conditions were rough at first, but by the time the baby came, she was already basically a part of the family. And now, you are joining them again, this time as a new girl, Emily.