While I am not in this boat, you should end the project if the returns from it (projected into the future if needed) are not more than whatever else you could gain with the time and money you are putting into this project, plus the stress you are dealing with, if any. Comparison to day job is not valid at least directly.
For example, if you are putting in T hours of time per day and M amount of money, think about what is the realistic value you could reap from that time and money, taking everything into account. Whatever is expected to give higher returns for your efforts, resources and stress, should be what you do.
Apologies if I stated something that you find obvious.