If you’re determined to maintain a relationship with this “partner” rather than simply withdrawing completely as most of us suggested, then …
I suggest you have a conversation with him and let him know flatly that if he carries through on his implied threat to harm you or anyone else that he stands to lose everything: 100% of his investment, 100% of his reputation, and 100% of his time for however long he is imprisoned as a result of his acts. He can certainly kill you, but it won’t resolve his problem. He has to “understand” this, as it seems that his anger is preventing him from that simple understanding.
Once he understands that basic fact, and if he can calm himself to discuss a rational way forward, then you also have to get him to realize that you will not work “under orders” or under any other threat of compulsion or likely future harm. Again, remind him that he can shoot you – any of us could be shot by various people at any time – we need to rely on the people around us being more or less rational actors. So keep moving him towards being analytic and rational about the problems you both face.
So, now presumably you’re not a target for his violent revenge and the relationship has been redefined to where you are no longer his minion or slave, but a notionally equal partner. (It’s going to be up to you to continue to reinforce this. My sense of things from what you have said before is that he is apt to go his own way, do his own thing, and rely on force or threatened violent force to achieve compliance. I still would not trust such a person, but you seem intent upon continuing some kind of business relationship.)
At this point in the relationship: you not being threatened with death, not working as an employee or chattel slave, and now a full partner in the endeavor, then it would be a good time to discuss “what has to be done” to salvage the business. It would be better to discuss and agree first whether the business really can be salvaged, or whether the additional investment in time and money would be “good money chasing bad”. There comes a time in many businesses where rational actors have to look at “the world as it is” regardless of all sunk costs in time and money and make a dollars-and-sense decision as to whether it makes sense to continue. It may not make sense, and if it doesn’t make sense to you, then you should refuse future participation – under the terms outlined above.
That is, when equal partners dissolve a partnership because of a fundamental misunderstanding between them about the viability of the business, then there has to be a mechanism to dissolve it and for the partner who wishes to exit to sell his stake to the other, and the partners can otherwise walk away from each other. That’s just normal business.
So: after you’ve established an acceptable working relationship, determined (and agreed) what the future will require to get the business up and running again, but before you make a commitment of more time and/or money, you need to resolve what happened with the original stake. You have not said how much money was involved (it’s not important to us to know; I’m just saying that we don’t know), nor have you said the basis of the partnership, whether the money split was 50/50, or whether he put up the capital and you put up what we call “sweat equity” (that is, “where you do the work” in exchange for your share of the partnership).
If the money investment was all his, then it’s fair that he spent the bulk of it where he thought it should be spent. After all, rent is a valid business expense. However, as a partner you need to be informed, even if the money is all or mostly his, because that lets you know how the capital is invested and whether your effort has equal value to that – maybe it doesn’t, and that could be another source of friction. These things need to be out in the open in a partnership. On the other hand, if the money was “just spent” and there’s no good accounting, then he may be defrauding you. We just don’t know, and you’re not saying. (Not that I’m asking you to; it’s just more missing data in the problem.)
The expenditures need to be under control and agreed to by both (all) partners so that they know when and how the equity share of profits will be divided, and when business receipts will exceed expenses so that profits can be expected. This is all Business 101 stuff. He should realize this, and so should you. He can’t be making expenses you don’t know about. He can’t be making expenses that benefit him without benefiting the business. He can’t be making expenses at all – if you’re an equal partner and disagree with the items being purchased or the amounts being spent. This is basic partnership. A partner – unless he’s a managing or general partner in an unequal relationship – cannot be dictating terms to other equal partners.
If and only if all of the preceding can be worked out – and only you know how likely or unlikely that is – then you can decide together (it’s not all his decision, right?) what is to be done, the schedule and manner of accomplishment, the division of duties as to who-does-what, and the expected additional investment required from all parties. Again, this is basic partnership, basic business.
Personally, I still advise to dissolve the partnership and never look back on this. An individual who acts in the way you have described is beyond the pale. A “problem relationship” is one thing, and in business we have to be able to roll with all kinds of personalities and problems in a businesslike manner. But having a partner threaten – even indirectly – to shoot you for “business problems” is completely unacceptable. I would never work with or for such a person.