I am not yet in a place where I could walk into a venue and see him and his husband together in a couple-y way and be okay - but I'm a hardwired mono.
@Deverijni if you lived closer together, this might inevitably happen, accidentally or because of a social event he wanted you both to attend. How would you expect bf to handle this?
@Dagferi & @Magdyln, I didn't mention DADT in my OP for a reason--that's not the long term plan. If I get serious with someone, it's different. However, even once hubby knows I'm in a real relationship with someone else, should that occur, he still hopes to keep things VERY separate.
I'm not saying I expect them to be besties, nor would I expect hubby to let lover spend nights in my bed. But my husband says, for example, that if I have a party, I can only invite him or the other partner, not both. If I'm out with friends and my other partner is with us, I should not invite hubby, and vice-versa. This is the sort of thing that has me worried I'll feel split in two. Again, this person is hypothetical. And, my husband works a lot, so I'd have time and space, technically, to pull it off. But it's a small town, and at some point, husband and other WILL run into each other.