How do I call a person who's having a 1 on 1 conversation with me [duplicate]

I agree with the comments of @RonaldSole and @WS2, each of which points to interlocutor as a solid answer to the OP's question.

From Merriam-Webster:

interlocutor: a person who is having a conversation with you

Though it often has a more specific meaning for language learners participating in a language exchange, the term "conversation partner" can be used to refer to the other party in a one-on-one conversation.

Here's an example of it in use:

There are times when a conversation just doesn't seem to click. My conversation partner and I are not picking up on each other's cues. There's door after door that I do not wish to open. Well, I can certainly opt out and find a more palatable conversation partner. If social circumstances do not permit such an exit, I can always choose to converse about the present.

[Source: Infectious: How to Connect Deeply and Unleash the Energetic Leader Within by Achim Nowak]