> The App is almost done
I assume you've learned the importance of discussing these things up front. :) At this point, you should do your best to drive for clarity and written contracts before you continue your efforts. Your cofounder doesn't sound necessarily unreasonable, but just in case: Make sure you get everything in writing. Don't allow for infinite delays or vague future promises.
Most important question right now: What, if any, agreements do you two have in place? Did you make any agreements, written or otherwise, before you started building the app? I assume you used some of the assets he provided (wireframe designs, branding, logo) in the process, so it's too late to completely separate your app from his reach. Unless you're geared up for potentially years of legal challenges, ignore any advice to cut and run with the source code.
Second: What are your expected roles in the company going forward? Will he be running the company by himself and acting as President/CEO? I know you put a lot of work into the app, but an app alone is usually not sufficient to be a functioning business. If most of your work is done and his is just ramping up, then a 70%/30% split doesn't seem unreasonable.
I suggest you clearly define roles and expectations for both of you going forward. This will clear up a lot of the split.
> I believe a fair split is where I have at least 50% of the company
Greater than 50% means you're in charge of the company, effectively. Are you interested in running the company yourself? If not, pursuing greater than 50% ownership is not for you. Even in situations where cofounders agree to be equals, it's still often recommended to have one founder at 51% and the other at 49% to make it clear who gets the final vote. Do you want that to be you? Would he still be onboard if that was you?