"They let me go."
Translation:Ellos me dejaron ir.
Honest to God there is a paragraph in my book "Verbs that Do Not Ordinarily Take a Preposition When Followed by an Infinitive" There are fourteen of them! Dejar + infinitive to allow to, to let Examples Mi madre me dejó salir. My Mother allowed me to go out. Dejé caer mi libro. I dropped my book. (LiteralIy, allowed my book to fall.) So, to answer your question--you cannot use the preposition between verbs in this sentence.
I just put "Ellos me dejaron." is that wrong because it means "They left me."?
I don't get the 'ir' part. Why is 'ir' there at all? Wouldn't Ellos me dejaron ir translate to They left me be. It seems in addition to translating you have to also imagine the many possible applications. Context helps but it can still be vague or a bit of a stretch.