"For one moment he actually got me believing that he had aced his thesis"
Is this a proper usage of "got"? Or should it be "got me into believing"?
-First post btw. Thanks for any help! :)
I think "had" is more commonly used
For one moment he actually had me believing that he had aced his thesis
However, to get sb into sthing is usually used when saying you introduced someone to some pursuit or practice:
She was the one who got me into cycling
He got me into horse riding last summer
So of your two suggestions, the more correct is "got" as you suggest.
"Got me believing" is fine. It is quite informal: a more formal expression might be "made me believe", or "had me believing"