There are so many layers to the commentary it's kinda nuts. It can mean:
"Two people, at night" "Those two, growing close" "Together, leaning on each other." "Becoming a couple."
and the list goes on. And since it's written with Kana, choose the one you want.
I would argue that since the connecting particle in the phrase is の, it must be followed by a noun. And since よる is not connected to a nominalizing suffix such as こと or の, nor in a form such as より, it should follow that this particular よる must already be a noun, in this case "night," rather than the numerous different よる words that are verbs, i.e. "to lean against" or "to approach."
The intended interpretation should then be "the night of the two" or "the couple's night." Although it is much more romantic and fun to see it in an ambiguous light.
