What are the correct titles for the attendee/guest relationship?

Apologies for the horrible title.

If I'm invited to an event and I bring a plus one, they're are my guest and I am a guest of the event's host. But what am I to my guest?

I've tinkered with 'invitee' or 'attendee' and even had 'host' suggested to me.

Are any of these on the right track? If not, what are my options?

I don't think there is a term for the relationship you are asking about. If the original invitee's guest is a (potential future, not necessarily actual) romantic partner, then (in America, at least) the guest would be the invitee's date, and the term could be used in the inverse direction as well. This is only loosely tied to the fact of the original's host's invitation. But of course the guest might be a person to which date would be inappropriate, and then no term seems any where near right. If queried about it, a person would probably say something about being invited by the original invitee, being with them, etc, and would not try to name a particular role they fit into.

If I were the person who invited you plus one person of your choice, I would consider both you and your "plus-one" to be my guests, making no distinction between you. You could consider your plus-one to be your "companion" or "friend"; or "wife", "spousal unit", "significant other", "roommate", "old college buddy", etc. as whatever normal relationship there is between you calls for. As mgkrebbs says, I don't believe that there is any specific term extant for the situation described.