You need to hire an attorney, one who works in business litigation (if you can find someone specializing in minority shareholder disputes, that much the better). Right now. If you're delaying on this point out of some idea of wanting to "try to fix things first" or "not wanting to be the bad guy," you're just shooting yourself in the foot and downing blood thinners to keep the wound from clotting. Working with an att…
So if you get a whiff of partner's mischievous behaviour in past business dealings, it might be better striking out on your own or looking for other options.
As in being squeezed out get your partnership drawn up right after starting out on the project, whether you horizon for getting investments/public launch is 6 months or 2 years. After all you don't want to waste your time. If you don't have iron clad paper work covering you, most likely you have been played. If you are prepared for this then you would not have questions.
If the venture is out to grow big, talk to a lawyer and get the injunction against them so they can't proceed until they sort out your stake in the company, how much they owe and al the other business relates stuff. Also check if you have rights to the property you just might launch your own competitor product if there is nothing that explicitly forbids you from doing so. Savlage what you can, I am sure you can come out on top if you play your cards right and have honor in you intentions.