How to be supportive when you disagree??

I really struggle sometimes to be loving and supportive of my husband. He makes very rash decisions when he gets bored with work, life, whatever. Deciding to go back to school, wanting to find a new job and move cities (we just recently bought our house), start his own company, you name it. I want to support him but also feel like a lot of the decisions he tries to make, he makes largely without me or disregarding my opinion. Even when I make it clear that I don’t think it’s a good idea for us right now financially, good for us in general, or for our relationship. He’ll “agree” with me until the dust settles then just do what he originally wanted to do. I don’t want to be a witch and shut down everything he’s excited about or passionate about, I want to love and support him, but I crave a sense of settled and consistency in our relationship and just don’t agree with a lot of his decisions. Where do I go from here?