get (something) off (one's) chest
To reveal or discuss something that has caused one emotional discomfort and that one has repressed, kept hidden, or neglected to discuss earlier. I'm sorry but I just have to get something off my chest. How could you treat me like that last night?
off one's chest, get
Relieve one's mind by confessing or saying something that has been repressed. For example, I've got to get this off my chest-I can't stand his parents, or He admitted taking the dollar and said he was glad to get it off his chest. This expression uses chest for the seat of the emotions. [c. 1900]