What is sacred to us are the things that are most important to us. When we share these parts of ourselves we become exposed and vulnerable. We have an emotional and spiritual need to share these sacred things with people. This is what intimacy and closeness is. I refer to this as allowing them into our "sacred space."
It seems that something so important and vulnerable as allowing someone into your sacred space ought to have some ground rules. The number one parameter for someone in your sacred space is that they respect and honor what is sacred to you. This is not a place for them to criticize, make fun of, or disagree with what is sacred to you. This is not about them. They are in your world now. They are either able to accept and respect what is sacred to you or they are not.
If they are not able to respect your sacred space, it is your responsibility to yourself to get them out immediately. This is called "keeping yourself intact." They have lost the privilege to share that most beautiful part of you. Not removing them and protecting this vulnerable part of yourself leads to deep emotional wounds and difficulty trusting people.
Removing them from your sacred space is doing whatever it takes to take away the ability for them to continue to disrespect that sacred part of you. There is no correct way to do this. This is not about assertiveness or honest communication. This is damage control. You may not be feeling especially strong after someone just violated your trust. You may be in shock. Saying something as as simple as, "I have to get going now," or, "It is getting late." could work. You could change the subject or simply leave. You can confront them or explain things to them later, but this will not happen in the middle of your sacred space.
It seems only fair when you do that most courageous act of sharing yourself, you do so in a manner that keeps you intact. Ultimately, this leads to trusting yourself (to keep yourself intact), so you can share again another day.