I cried for 15 minutes because someone stole my post and got gilded
Has this happened before?
No but they're such a jerk for taking something that wasn't their idea.
It's understandable that you would be hurt by someone taking your idea. No one should steal ideas from others. In the future, you can prevent your post from being stolen by only allowing certain people to see it.
But then how would the whole Reddit community see my post?
You can try to flag the stolen post or post a link to the original. If other people se the unfair behavior they might down vote the thief's post.