Flexbox : How to make left column decide height of right column

Hello everyone,

I’m currently trying to replicate the layout of the hero section in the image below but to no avail.
Imgur

Right now, I have my images at 100% height which stretches them and I don’t want that. Can anyone with a better understanding of flex help me with this? I’d like it if the left image was the one which affects the height of the right column with it’s images.

Here is my site Read-Only: LINK