He has a spending problem and I want to leave

So I've posted on here before about some troubles I was having with my fiance. He spends money frivolously and doesn't think about the long term effects. He makes more than enough money to pay his portion of the bills with at least an extra 300 dollars for savings. I told him a few weeks ago that I'm not happy with our relationship because the strain of his spending and the struggling unnecessarily is beyond infuriating and just down right irresponsible. We have a two year old and a baby that will be here within the next 4 weeks. I told him a few weeks ago that if he didn't start making changes and start being more responsible with his money then I wont stay. I will walk away with the kids because they don't deserve to live in an environment where we struggle to pay rent every month. Am I wrong? Was I too harsh in my wording? I'm just so fed up and I've always bailed him out when he couldn't afford his portion of the bills but I'm just over it now.