Ah.... when you're together it's on and when you're not it's off...
To me, that says that he's either cheating or wants something very, very casual.
It's interesting that you've only been able to see him at conferences. It could be absolutely open with his partner... or could it be that he has an excuse to be away because of work?
Do you know for sure that she knows about you?
If she does, I think it's time to guard yourself.
It sounds like he's telling you what he wants.... and possibly you're not taking it in because you want to believe something else? I don't mean that harshly, we all do it sometimes.
I definitely think you need to have a talk with him... possibly consider withdrawing yourself from the situation if your feelings are getting to deep. It definitely sounds, from what you've written, that you want different things.
Me: (30f) open poly
GF: (40f) My long-term, long-distance partner
Hubby (37m): GF's husband
Garcon (26m): GF's submissive/third partner
“Peace comes from within. Do not seek it without." ~ Buddha