Firstly, congratulations on sparking such a robust discussion! At the risk of oversimplifying, it seems the responses fall into two veins:
A: As Jerome stated, personal commitments must be honored and that is a very basic tenet of any business relationship. If you really feel that this friend of yours gave a personal guarantee and then did not follow through, that is a red flag (or at least a yellow one).
B: As many of us have mentioned, your enterprise is NOT a non-profit or volunteer organization so your friend's motivation to help you is probably linked to his belief in a realistic financial benefit.
This sounds like it could be a situation where a friend wants to help but does not have any clear motivation to do so.
The only way to find out is to grab a coffee as Ema suggested. Rekindle your friendship and try to gain clarity about what your friend can and cannot promise to do given that there is no cash salary available. Also, as others have suggested, try to convert this from a handshake discussion into a written agreement with a firm commitment to give equity in return for well defined deliverables.