Talkative

to keep talking about a certain subject in length, particularly in a way that bores others

She could go on and on about her favorite TV show for hours.

to enjoy having lengthy and non-sensical conversations with people

There's some guy at the other end of the bar running off at the mouth about how far he can throw a football.

to speak in a manner that is lengthy, continuous, and annoying

He is talking a blue streak about his new project.

someone who shares someone's secrets and private matters with others

Don't tell Sarah any secrets; she has a big mouth and can't keep anything confidential.

to continuously talk, particularly in a way that annoys others

During the meeting, our boss talked the hind leg off a donkey, going on tangents and discussing unrelated topics.