Cranberry, maybe you need to just take a break from this relationship. The wife is having a tough pregnancy, is moody and grouchy. The husband sounds like he's trying to be supportive while his wife goes through a tough time.
Maybe you should return after the kid is born. Perhaps you could help out with some food, or watching the kid, changing a diaper here and there. Just pop in to drop off a casserole or something, don't stay too long.