Gender neutral pronouns and private conversations

I was having a conversation with my girlfriend today and she briefly spoke about a person who happens to be trans. Let’s call this person ‘Eric’. As I listened to my girlfriend speak, I learnt that Eric goes by the pronoun ‘they’. She didn’t mention this to me, but I understood this from what she was telling me.
Here is my opinion on this super-hot-debated topic from three years ago, that I don’t understand very much about as a boring cisgender person:-
I will honour somebody’s request to use any pronoun they ask me to, because I think that is basic human decency. Somebody prefers to be called a certain way, you call them that. Basic human decency is very appealing to me. So, if somebody’s pronouns are ‘they/them’, I will use that while—speaking to them, speaking about them to others in their presence, speaking to their acquaintances in their absence, addressing a crowd, in my writing—always. That does not change. My opinion is formed on that.
However—here it comes—when I am speaking about Eric (when Eric is not around) in absolute privacy, like when I was speaking to my girlfriend, where I trust that the person I am speaking with is not going to judge/mock Eric’s preferred pronouns, then I may use a binary pronoun (he or she) while talking about them. That is, I will—in all probability—refer to Eric as ‘he’ in my private conversations, solely because it is jarring, inconvenient and sometimes downright confusing to keep saying ‘they’ in the said conversation.
And I think that is OK.
Here’s why—firstly, Eric isn’t hearing me use the pronoun ‘he’. So I am not being disrespectful to Eric. Secondly, the fact that Eric identifies as non-binary is not something that I need to constantly validate in my private conversation. I don’t think my private conversations have that kind of a bearing on Eric’s gender identity. Thirdly, I respect and support whatever somebody wants to be in this world. But asking someone to radically change the way they speak in private is a very big ask, if not problematic.
Why am I willing to speak one way in public and another way in private? Because I don't wear a suit to bed and I don't turn up to work in my underwear. Public and private lives are different for most people.
I am not going to be OK with somebody telling me how I should use words, what I see as perfectly noble words, in private. What I construe as ‘disrespectful’ in my private conversation, fortunately or unfortunately, will always be up to me.
Even though I will always refuse to partake in conversations that mock somebody’s preferred pronouns in their absence, I will, however, call Eric a c#nt, if they have acted like one with me.
And that, usually, is far far worse.
(I should make it clear that my girlfriend totally disagrees with me. And, as always, I am open to further discussion. Write to me.)