I am not good at finance. My thought is,

1) Your money is an investment in the LLC, i.e., part of the funding. If LLC fails, you could lost your principal. In this case, you should be able to share the profit based on the total investment.
Or,
2) You give them a loan, and earn fixed interests. In this case, your friend should use some equity to guarantee your loan, like you get house loan.

From what you said, I do not think it is a fair deal to you.

Again, I am not good at finance. I could be wrong.