Didn't think of that!
Tell you what…When I send my ex-wife her money…you can lick the stamps.

I think Alice found the mask and thought it was a kinky idea for her husband to FUCK her while wearing it. And I think the last thing she expected was for him to have an emotional breakdown and his guilty conscience confess everything he did that night, and his lies and that party and the dead hooker.

I think it was meant to be a sort of final warning for Bill to let him know that they could break into his house and get him and his family whenever they want to if he doesn't stop his inquiry into the truth behind the masked ritual.

yes, that is what they implied.

Oh thanks I forgot that part, so it was Alice and not the organization people, but I don't think she confronted him, he just spilled his guts, she was the one who felt guilty after her sex orgy dream.

Elaborate of Alice in that case. He comes and goes from home before that scene.
Buy The Ticket, Take The Ride

When Bill got home from the masked ritual orgy, he opened a cabinet, removed a box or case, and stuffed the bag with the costume and mask into the cabinet. But he left the box he took out sitting on top of the cabinet, in plain sight. Alice no doubt saw it and opened the cabinet to put it away, and thereby found the costume and mask. She took the mask, planning to confront him and find out what he had been up to. When Bill returned the costume, the mask was not there, so he paid Millich for it, thinking he must have lost it. The next night when he came home, Alice had placed the mask on his pillow to force him to acknowledge he'd been up to something, and let him know she knew it.

No. He didn't have the mask as Milichi Told him so.

Yes it`s a great film I shudder at people who find it "boring" Clearly they've never had a relationship or any significant adult experience.
I'm still picking my brains if we do or don't see him return the mask as well as cloak(which we know he gave the cloak back) to Mr. Millich. I'll have to re-watch it.

It cannot be stated for certain how the mask got placed on the pillow beside Alicethere are plenty of theories about it, but that's all they are: theories.
When I first saw EWS, I pondered this bit from the film for quite a while. I wondered whether it was there because the shadow group meant it as a warning message to Bill, or did Alice find it and put it there before napping? I think a case can be meant for either conclusion, but like so much else in EWS, the ultimate explanation eludes being definitive. That's one of the great things about this film, in my opinionit's intentionally complex ambiguity.
"I was cured all right!"

I`m not sure she wanted him busted, as she never had any notion to believe he was up to anything, other than the 2 models at Zieglers party which he already explained..
Yes I remember he stashed the mask and cloak in his cabinet, but I thought he returned both to Milliche?

The mask is like the locked pantry door in the Shining - it's a symbol of a nexus point between two realities - in Kubrick films this is often a character's subjective world view being deconstructed or reconstructed (or anything in between). For Bill, this is the symbol of his fractured reality - of his 'dream' world and his 'real world' colliding - the worlds colliding theory if you are familiar with Seinfeld.
I don't think Alice put the mask there, but it's possible. It looks oddly weighted on the pillow, which seems to be sinking a little under the weight - an uncanny suggestion of an invisible body, which is a perfect metaphor for Bill's fear of his place in Alice's fantasy realm, his anxiety over his own desires and ego and what not.
Like a lot of things in the film, it's a symbol that challenges what we consider to be literal.
Buy The Ticket, Take The Ride

There was a scene where he stashed the mask real quick in a dresser I believe.

She wanted to "get him" busted by putting it there as a symbolic thing. It's something most women would do. He had some explaining to do and spilled his guts and tears.
Now, wheather she knew about the whole ritual party herself, I don't know.

Ah so he forgot to return it, what do you mean it worked?

No. Alice found it in the dresser and put it there for Bill to see. It worked..