Cofounder randomly deciding to go part time when he was supposed to commit

To set some context, me and my cofounder started a company in June 2024. I was responsible for the technical development and he handles the business part of it. We each own roughly the same stake. I was working on the idea full time and he was working part time since he was still working. He dropped his resignation letter in sept but work demanded him to work for another 3 months due to an employment clause before he was relieved - This was all fine with me since this was communicated to me before hand. I built the MVP out in about 5 weeks but sales was lagging - the product exists but no one knows about it. His last day of work was in the last week of December and I was really excited to give it our all for the company's growth. Today he drops the bomb shell that he is going to continue working part time on the company because he got selected into a fellowship at a top tier venue. He claims he needs 6 more months before he fully commits to the company. I don't like this, I honestly feel cheated at this point. I have waited 6 months for this (and worked on this for more than 8 months unpaid/unemployed) only for him to say he needs 6 more. When I enquired when he applied to this fellowship, he says it was after we incorporated the company and applied thinking it was a part time role (where you spend few hours a week) but the role which was offered to him now is a full time one. How do I go about this ? Should I just call it quits and look for a job ? What would you do ?