The Psychology Behind "I never said that, you are imagining things."
The Psychology: This is the textbook definition of Gaslighting. By flatly denying reality, he is attacking your perception of sanity.
Subconscious Intent: He isn't just defending himself; he is actively trying to rewrite history.
How to Respond
Do not argue about facts. Simply state: 'I know what I heard.' Then, start documenting conversations (screenshots/notes) immediately. Trust your memory.