Hummmm I think maybe it's worth reconsidering you going with him to OZ before you dismiss me completely think about this.....
If you go too you can spend some time talking and thinking about your future, you get a break from normal day to day as well as some quality time with your dh.
I know at the moment you are annoyed with him but this could be your chance to have some time with him to sort things out so that he understands you more and so that he understands what he needs to do to make sure his family are happy.
I know you think you can't leave your dc's but in the grand scheme of things it's only for 7 days out of their whole lives and they will probably be having so much fun being looked after by granny (or whoever?) that they won't mind so much, sometimes a decent break can really make you re-think things and for your dh it could pull you closer together, for you and the dc's they will appreciate you more because they will have had chance to miss you and you will have had a break from constantly doing washing cooking cleaning, splitting up arguements, tripping on toys and will have a chance to get some passion with your dh perhaps?
For me personally I agree with the statements
"sometimes a change is as good as a rest"
"absence makes the heart grow fonder"
"if mum is happy everybody is happy"
If you can't beat em join em?
As for BF 18mth old I can see how this is an issue and I haven't bf for that long so have no idea how you would handle that tbh (well done btw) but the point here is if there are issues with your dh it's better imho that you spend 7 days away with him sorting them out than 7 days at home resenting him even more and possibly your relationship getting damaged.
Yes I know he could possibly just not go to australia which would mean he could be at home with you and the dc's but let's face it, he's a man, if it ain't broke as far as he's concerned he's not going to see the need to fix it is he? It's also quite an opportunity to go to Oz and not have to pay for it and I would want to go too if I was him, wouldn't you if the shoe were on the other foot?
Now you can tell me to shut up and stop waffling I'm just adding my 2 penceworth and I could be totally wrong.