Constantly destabilizing me

I've been with my boyfriend over a decade now. We found out he has ADHD a few years ago but he doesnt like taking the drugs for it. He said they made his heart race and he didn't like it. 

The problem at the moment is that we are getting older and I want to buy a house and start a family soon. We are getting married as well and I thought that would be the start of a bit of a chain that would get us into a settled family life. For years now one of his big ADHD traits has been impulsiveness without action. What I mean is that over and over again he will come up with crazy plans about what he wants to do with his life but then does nothing about it, then later blames me and says I held him back because of my job/friends/lifestyle. He says he hates his job so he wants to move abroad and start a random business but he has no plan. I feel like Ive tried everything - being supportive of this stuff because I dont want to seem like I dont care but then nothing ever happens about it. Its a cyce and now I just won't entertain the conversation any more and then we argue that he says I dont care about his dreams or believe in him and resents me for "holding him back". This did stop for a while but over the last week he has had an argument with his new boss and its now all being dragged up again. I should say that we are also half way through planning our wedding and he now is saying he wants to move abroad and start a business or "take a year out" and travel but again theres no plan.

I thought as we are planning our wedding things might be different now. He might grow up and stop what I cant help but see as childish fantasies but they seem to be getting worse. He has even said things about spending all his (soon to be our) savings from years of hard work on moving abroad and setting up this business and working for himself. This is money I thought would go to our first home.

I dont think he realises (or maybe doesnt care) how much this effects my mental health.  I find the cycle of suddenly wanting to pack up our whole life and spend all our money on a whim very destabilizing even if it has been a long term thing he wants. I dont know whether we're settling down to have a family or packing our bags and moving abroad and it hurts me that he cant see thats hard for me. At the same time it feels like if I don't support these whims, I am being a horrible unsupportive partner who doesn't believe in him. I just cant pretend to support something I know he will have got over in a few weeks but also that I definitely dont want. I wish he could understand that every time he does this it pushes me a little further away. I need security in my life emotionally and financially and is a real struggle for me.