Personally, I think you may have already gotten a great deal if the angel/co-founder is willing to do a 50-50 split and not take a salary (or get paid in equity in lieu of salary.) Is your co-founder now demanding to be paid in salary/equity after they agreed (I assume this is written down somewhere?) otherwise? If this is a "handshake agreement" situation, then I guess you are in the process of learning an important business lesson...

That said, fairness in business has nothing to do with your or your co-founder's personal financial situation, other than the constraints of reality (i.e., you simply can't work without a minimum amount of salary.) Frankly your co-founder should be paid in something (equity) if they are not drawing a salary. Theoretically, ownership and compensation should reflect what each of you are bringing to the company. In fact, your co-founder is actually getting compensated less than you while investing their own money - that means you are already better compensated than them. Is that "fair"? Maybe, maybe not, you guys have to agree.

But get a written agreement - if this already exists than just stand by it.