Oh, Bones... I remember dear Mr. Blueberry. Sounds like he needs a crash course in Remedial Romance 101!
Good for you, for telling him straight up what the problem is.
You know him best, but if he's just an ordinary guy... I'd say the fact that he's clueless

pretty much comes with the territory

and he's not unique in that. Takes alot of instruction to
housebreak ermm... I mean, train... a male

and I'm only partly kiddin!
((((((((((((Bones)))))))))))))) here's one possibility:
sometimes, I've found, when they make an announcement/hoopla like Mr. B did about this dinner date, they're testing the waters and feeling out your reaction.
If you keep it low-key and don't gush all over the place about their ideas, they may decide that it's not really a big deal to you after all, so no harm done if they renig. I know, I know... it's frustrating, but from my experience, he'll always take the path of least resistance... so if I don't show enough excitement about a proposal, that may be the last time I hear a word about it.
Unless, maybe, he was about to pop the question on that date and then chickened out.

Oh, how my mind doth wander!
Well, either way, he needs that crash course, for sure!
If you've the patience, he may be educable!
Love,
Carolyn