Nouryia, thank you for your kind and thoughtful reply. Things have been moving pretty quickly, which is unsettling...but we've talked a lot recently, and he's been reassuring, which is very good. I think I just need time to get used to the idea. I asked my husband if I was like this when he started dating his current girlfriend, and he said yes.
I just think I need to work on the way I handle change.
As for the mentioning of the new person in an intimate moment...gah. That stung. And I've made it clear to him before that it makes me uncomfortable. But I'll try your suggestion - thanks!