Have you considered going to the conference yourself, even just part of it?
The unknown is likely to be much, much scarier than the known. You can think of it as a way of learning more about your bf and where he's coming from.
I don't know the Open SF conference, myself, but a look at the website suggest its much more about talking and learning than about hooking up.
As for the session that makes your eyes well up, the description doesn't seem so very scary:
The workshop welcomes 1) people who are willing to share their personal experiences, either successful or not, in navigating the challenges of connecting with people who do or did not share their desire for an open relationship, and 2) people who have questions about how these relationships can be approached or wonder whether they are worth the trouble.
This suggests, to me at least, that the session will be a forum for discovering how mono/poly relationships can
succeed; the answer to whether "these relationships" (not, I hasten to point out people) are "worth the trouble" could well be "yes!" Otherwise, why would they have the session at all?
If you were to attend that session, and were willing to speak up, you could contribute your own experience - and your insecurities about Open SF! - to the conversation. That might be very useful to the other participants.