Idioms that mean "to tell [someone] everything." or "to tell one's innermost feelings and secrets"..?

Spill the beans

Bare your heart.

Freudian Slip.

To let the cat out of the bag.

.

To give the game away.

bare your soul
come clean
let it all hang out
tell all
open up, open up all the way

@zensky, “letting the cat out of the bag” means to reveal a particular secret, to speak out of turn and let something slip that you shouldn’t. It’s not the same as opening up to someone.

It’s close and all the good one’s were taken. I was going to say bare your soul, too, but saw you typing and knew you’d write that one.

Wear your heart on your sleeve.

emotional strip tease

It’s not an idiom, but the word “divulge” is a useful one…

spill your guts

pick up sticks (gamer slang)

Purging your vault or pouring your core.

Pour out your heart.

Laying all your cards on the table

Open the floodgates?
Expose oneself
Hang the banner?
Sending smoke signals?
Straight from the horse’s mouth?
Be transparent or letting someone see through you
Showing the man behind the curtain
Opening one’s inner sanctum
Dropping one’s pants
Letting the barbarians in
Taking one’s mask off
Singing
Rolling everything out in the open
Opening the corral

Howay, spit it arl oot man!

Showing one’s true colors.

Purge the layers.
Unveil one’s innards.
Divulge one’s soul.
Expose one’s guts.
Knock down one’s walls?

Share your soul.

strip down to your skivvies

open the floodgates

“let your light shine” can be a way of saying “express yourself,” especially to someone who is shy or timid and likes to stay in the background.

Actually, I think the usual phrase I was thinking of is ”Bare your soul.”
Memory isn’t always accurate..

Mind-melding.