I actually think now, that like so many who claim that their DH/partner is 'really lovely', that he's actually no such thing, and as often the case in this type of relationship, you are actually scared of talking to him for fear of him kicking off. If that's NOT the case, then I think you're being a bit pathetic, in not speaking up and telling him what you NEED!!
As for him getting a lift to the wedding with your neighbours, how on earth do you think he'll get home even if he stay's sober, as obviously the neighbours will be drinking, hence he would need to have a completely reliable, alternative way of getting back to you should he be needed.
I think the whole situation is ridiculous, and as parents of two children already, I would have expected a far more mature resolution to what in reality, is a very simple situation.
Here's what I suggest -
You TALK to your DH - tell him you want him to stay with you as you are feeling anxious about the pregnancy with everything that's going on at present, and really feel you need him with you. If he argues with this, then tell him you might think I'm being irrational, but it's the way I feel, and THAT IS WHAT'S IMPORTANT!
He then acts as a husband, and says 'OK sweetheart, no problem, it's only a neighbours wedding, and not even someone I talk to that often, I won't go.
THE END!