I am not an investor nor a lawyer but if I was on the other end, I'd want open honesty regardless. I would explain the situation to them exactly as you did here

I am not an investor nor a lawyer but if I was on the other end, I'd want open honesty regardless. I would explain the situation to them exactly as you did here. I would include the comment about how he was invaluable to getting the MVP done as you mentioned in the comment but you have confidence in doing this moving forward solo and why. Discuss in advanced with your former cofounder about what he expects shares, if any, for his contribution this far so you have something to let the angels know. In reality if you guys did things right and was on a proper vesting schedule he wouldn't vest anything unless it was past the one year cliff period. Either way, know your numbers cold and a solid plan of action from here on out. Any hard data you can get from now till the meeting is much better than what you project i.e. sign ups of interest, paying customers, launch trajectory, etc.. Best of luck