Are the expectations originally outlined realistic? If your equity partner's responsibility is to deliver customers, but he's finding that there is minimal desire for your product/service, his ability to deliver is hampered.
I suggest a non-judgemental conversation where you discuss what, if any, obstacles he is encountering or if his interest in your company mission has changed. Often equity partnerships can be dissolved amicably, but do invest money to do so legally. You do not want to hold future earnings hostage.