My abusive ex regularly used to gaslight me like this. "I don't remember doing that." "I don't remember saying that." "You never told me that." "You were meant to do that, not me." "You told me [insert thing I never said]". A clever strategy because of course people forget things from time to time, right? So I tried to give him the benefit of the doubt. But over time I started to feel like I was going crazy.
I got around it by keeping a detailed journal and quite soon it became obvious how badly he was messing with me.
The strategy is designed to fuck with you and make you doubt yourself, while hiding whatever unpleasant thing they are doing/have done, or denying their own unpleasant personality characteristics.
The thing is, I shouldn't have needed to go through the process of keeping a journal. I just wasn't looking at the situation the right way.
It wasn't my ex's 'forgetting' that was important, it was that he was using 'forgetting' (either his own, or implying that my memory was faulty) as a tool to evade responsibility and put blame on me. If a person who acts in good faith honestly forgets something, they will be keen to remedy the situation.
Your partner is treating you as an antagonist and is mocking you when you raise an issue. You don't need to know exactly who is 'right' and who is 'wrong', you need to understand is that he is not showing love, care and a willingness to work together to resolve things when you raise issues with him.