Argthtjtr

There's a word for something, that when remembered--or a person that when spoken to--brings you back to reality and the knowledge that you're not insane. I keep wanting to say "touchstone", but I don't think that's it. "Cornerstone" kind of works (and is probably why "touchstone" comes to mind), but is more about a foundation you build yourself upon, rather than something you come back to.

I think I'm looking for a synonym for reality check. It's also the opposite of something that gaslights you.

An anchor:

A person or thing that provides stability or confidence in an otherwise uncertain situation.

‘the European Community is the economic anchor of the New Europe’

[Oxford]

If you're comfortable with a movie reference, like "Gaslight" itself, I suggest "totem", as used in the movie Inception:

A Totem is an object that is used to test if oneself is in one's own reality (dream or non-dream) and not in another person's dream.

[inception.wikia.com]

His raison d'être, his family's plight, when remembered brought
him back reality and sanity.

raison d'être. TFD

The fundamental reason for something or someone to exist; the sole or
most important purpose for someone or something.

Could you be thinking of lodestone?

Oxford Dictionaries

Lodestone: A person or thing that is the focus of attention or attraction.

A number of idioms or expressions might work here. I might choose the idiomatic expressions the light in the dark or the beacon in the fog to refer to a person or belief that acts as a waypoint in navigating (such as sifting through what could be considered a web of lies).

Likewise, the idiomatic "location" you'd return to when checking in with your person or belief would be home, or your center, possibly your home base. They act as a tether and as a ground for you.

Ironically, "touchstone" actually was the word I was looking for. I just happened to be rereading the book from which I learned the word last night.

From The Wise Man's Fear by Patrick Rothfus:

Simmon gave a relieved smile and nodded encouragingly. “That’s it exactly. All your inhibitions have been sliced off so cleanly you can’t even tell they’re gone. But everything else is the same. You’re steady, articulate, and rational.”

“You’re patronizing me,” I said, pointing at him with the knife. “Don’t.”

He blinked. “Fair enough. Can you think of a solution to the problem?”

“Of course. I need some sort of behavioral touchstone. You’re going to need to be my compass because you still have your filters in place.”

I took its definition from context, rather than the dictionary, so I was wrong about its meaning, but it was the word I was looking for.