The definition of get something off your chest is:
(verb) to tell someone about your feelings or emotions, especially after not speaking for a long time
Mom: I need to get something off my chest. I hate your new boyfriend!
Daughter: But I love him!
A: Dad, I don’t want to study Law anymore. I want to be a dancer.
B: How long have you felt this way?
A: For 2 years. I’m only getting it off my chest now because I didn’t want to disappoint you.
B: You can never disappoint me, son!
Stuart’s roommate got something off his chest last night when he told Stuart that he was too messy.