The first step is to talk to your coworker and tell them your concerns in a way that is not criticizing them or makes them even more difficult to work with. You

The first step is to talk to your coworker and tell them your concerns in a way that is not criticizing them or makes them even more difficult to work with. You can also try and socialize outside of work: grab a few beers and get their point of view. If they continue to be hard to work with, escalate to management and outline your concerns. What you really want to say to management is that your ability to perform at 100% is affected by this coworker / arrangement / situation, and you are being obstructed from providing the most value you otherwise could to the company. Any sensible manager would immediately address the issue, as he/she will recognize that your output is affected and the company is getting less value from you due to this arrangement.