Well based on what you've stated here, it seems that your ex has decided he wants to get his life together before he brings you into it for the long haul. Effectively, he's not happy where he is and with what he's accomplished, and having you at front and center of that life isn't fair to you and might cloud his ability to become the man he wants to be.
This is just one of those fundamental differences between men and women and a lot of it has to do with socialization. For instance, men are taught to be the breadwinners and decision makers, etc. We're supposed to be able to support a family. We tend to not feel comfortable in situations where we feel we're not bringing anything to the table. So instead of dating somebody seriously while trying to get our stuff together, we turn our entire focus (total tunnelvision) to success and THEN we find somebody to share that life with.
Women on the other hand tend to be happier with a mate coming along for the ride to the top. You all (most) tend to long for the support and companionship along the way. Effectively, the concern is building something together. Men, we like you to show up when we have something to show you like, "look, I've built this for you."
That just is what it is. You might not get it and it might seem ridiculous, but think about how we raise boys. To be independent, goal oriented, achievers. We teach men to focus on the doing things like a man. And we teach women to be compassionate supporters and backbones to a strong man. A strong man isn't one who's questioning himself while he tries to get his stuff together and can't support you.
There's a whole lot of built in insecurities that have nothing to do with you or women in general there, but it really is just the aftershocks of the way we expect most men to be.
Not saying its right, but it is really just how most of us men view life. If we aren't financially stable or we're just not in a good space, we aren't ready. Period.