Hello,
I will attempt to assist you here but I for one, don't use event sheets and two, you have two contradicting statements.
have a boolean that makes the player change Y position. But once it does, it is stuck on the Y position I just gave him.
How can I make this event only play once? (Set Y, and then leave the player on its own again ¿?)
Looking at your event sheet I am going to assume the player is stuck at the first Y position.
You have 4 individual conditions, and they all run once, apart from the first condition where your setting your X position.
You can have multiple conditions to an action. Here is what I think I understand you need to do.
Condition #1 - Keep as it is.
Condition #2 - Add a second condition to it. So it's Every tick & On Space pressed.
Condition #3 - Add a second condition to it. So it's Every tick & Is Boolean.
Condition #4 - Keep as it is.
Something like this: