My close friend and I have undertaken a Machine Learning project with the potential to generate some amount of income. Both of us are technically competent and when collaborating everything runs smoothly and we have no issues.
The problem I'm having is that my colleague and I seem to have vastly differing levels of commitment to this project. This is not surprising, given he is still an undergraduate and I have recently graduated - I feel as though being unemployed is making me hungry for this project to succeed and am not afraid of putting in late nights developing and bugfixing.
What is bothering me is my partners lackadaisical attitude to the project: one example is him pushing an update that breaks a critical data collection script and then go AWOL on holiday for a month leaving me to fix his code!
I have had to learn other programming languages simply to bugfix his work on such occasions and this has consumed the vast majority of my time spent on the project, leaving me feeling utterly drained and demoralized. He has repeatedly promised that he will dedicate more effort into the project (this has been going on for months) and yet I see no change in his behaviour.
How do I take ownership of the situation give him the ultimatum of:
"If you're going to be in this with me I need your help, otherwise I'm happy to finish this project on my own"
without coming off as abrasive and potentially losing a valued friend?
Startup partner is doing more harm than good to our project and I'm losing my mind