Corrections in red.  Stylistics in blue.

Jump into a Puddle.  Capitalize the first, last, and all the other words in a title, except for articles, prepositions, coordinating conjunctions, and the word "to" in infinitives of verbs.

I had been standing on my balcony when I saw a couple who were walking at the courtyard. So romantic.

And then the young man said: "Well, on the count of three. One. Two. Three!". They scattered ?? and jumped into a puddle. After they cleaned themselves [Good variant: .. after they cleaned up], they continued walking. I guess they found each other.

For such a romantic moment the word "guy" sounds too unromantic.  "young man" fits in better.

I don't think the couple "scattered."  "To scatter" means to separate in different directions.  These love birds probably were holding hands when they jumped into the puddle.  To get a mental image of what it is to scatter, imagine a flock of pigeons on the lawn, and suddenly a cat appears.