Thanks to the others for explaining vesting, they are spot in.
Basically, you don't want to end up in a situation where your co-founder can take off after 6 months and still have 50% of the company. Co-founder==co-worker, in the strictest sense.
Conversely, if the $8k is to be treated as just investment (which would not fall under vesting) he should be taking much less than 50%.
It's not just an investment though, the OP has committed to doing some serious marketing, let's say at least equal to the amount of work that the dev co-founder puts in to create the product in the first place.
From what I read, he was committing $3k towards marketing and gathering users, but did not specify how much work he'd personally do. Just want to make sure any people new to this ask the right questions up front, I'm not implying that hmexx is trying to screw anyone
Basically, you don't want to end up in a situation where your co-founder can take off after 6 months and still have 50% of the company. Co-founder==co-worker, in the strictest sense.
Conversely, if the $8k is to be treated as just investment (which would not fall under vesting) he should be taking much less than 50%.