It sounds like you're getting frustrated with the process (working with other people on an open source project), but you should really just let the process work _for_ you, not against you.

Work with your community (which might just be this single developer at this point) to collaboratively create a style guide or a set of standards for all future code submissions. This will be an outlet for you to professionally air your grievances and allow them to see where you're coming from. Simultaneously, this might provide you with some additional context that could help you better support them.

Best of luck!