There are a couple ways to approach it, depending on your level of trust in the Ivy League co-founder: BRUTE FORCE APPROACH 1) stop working on the project -- at this point you have leverage because you have the code and the knowledge of the code, he does not. 2) make the code base unavailable 3) refuse to participate in fund raising, where he needs you (normally) as the tech cofounder to answer tech concerns raised by the investors

I'll stop there because there's a 'softer gentler' approach you can figure out by yourself.

I'm stopping there because he has already insinuated the following:

"I'm not convinced yet that I need you, software guy. It seemed easy enough to find a guy like you to code this up for me and I could probably do that again, especially once I raise funds and can actually pay someone to write code."

"If I was really willing to share the pie, I would have addressed your concern about "let's put the equity share in writing" but I sort of 'stone-walled' you on that because the risk of you bailing out now is minimal, you already provided me an MVP which I can show to investors to raise money."

I've been down this road before. Unless you have very unique technical know-how, you can be replaced by almost any other coder. And if you provide the work with no 'sharing agreement' you risk discovering that your non-technical co-founder shows he is not motivated -- by anything -- to later cut you in for a piece of the pie.

Let me say that another way. Put together an equity share paper. Put it in your own words and/or using equity share statements from the web. If he refuses to sign even that, you know where you stand, he's probably put you on his "expendable" list.

After the tech world saw Zuckerberg become a billionaire by absconding with 'not his idea', ethics and respectable business behavior is much less common, unfortunately.