Flexbox one child fills the right space - the others fill the left space

Question

.container {
  display: flex;
  flex-direction: column;
  flex-wrap: wrap;
  height: 500px;
}
.cell {
  background: #ccc;
  border: solid 3px black;
  width: 50%;
}
.cell-1 {
  flex-basis: 100%;
}
@media (max-width: 500px) {
  .container {
    flex-wrap: nowrap;
  }
  .cell {
    width: 100%;
  }
  .cell-1 {
    order: 2;
  }
  .cell-2 {
    order: 1;
  }
  .cell-3 {
    order: 3;
  }
}

<h1>Vertical Boxes</h1>
<p>Goal: Have one box on the left, and two boxes on the right that are stacked. All without nesting, so that the order of the boxes can be changed on smaller screen sizes.</p>
<div class="container">
  <div class="cell cell-1">
    <h2>One</h2>
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iusto pariatur rerum, illum accusantium cupiditate ipsam, eaque quae fugit cum assumenda ad. Modi, excepturi. Assumenda, nobis, consequatur? Aliquid repellendus quis, iure. Lorem ipsum dolor sit
    amet, consectetur adipisicing elit. Iusto pariatur rerum, illum accusantium cupiditate ipsam, eaque quae fugit cum assumenda ad. Modi, excepturi. Assumenda, nobis, consequatur? Aliquid repellendus quis, iure. Lorem ipsum dolor sit amet, consectetur
    adipisicing elit. Iusto pariatur rerum, illum accusantium cupiditate ipsam, eaque quae fugit cum assumenda ad. Modi, excepturi. Assumenda, nobis, consequatur? Aliquid repellendus quis, iure. Lorem ipsum dolor sit amet, consectetur adipisicing elit.
    Iusto pariatur rerum, illum accusantium cupiditate ipsam, eaque quae fugit cum assumenda ad. Modi, excepturi. Assumenda, nobis, consequatur? Aliquid repellendus quis, iure.
  </div>
  <div class="cell cell-2">
    <h2>Two</h2>
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iste mollitia temporibus id sint illum doloremque pariatur nulla vel soluta, nostrum vitae, suscipit ea natus sed eaque in velit deserunt deleniti!
  </div>
  <div class="cell cell-3">
    <h2>Three</h2>
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Impedit, architecto perferendis voluptatum accusantium est ipsam fugit, laudantium fugiat nostrum consectetur earum. Asperiores, similique deleniti nobis nemo error, iste iure architecto.
  </div>
</div>

I'm a beginner in CSS/HTML and need some advice. Is there a way in flexbox to force multiple children to remain on the left and only one to fill the whole space vertically to the right like in the picture? I have posted an example code I've found here which is a mirrored example, but I don't want to set a predetermined height. Or should I be using something else? Thanks.