Some background information: I've gone to the same chain of gyms for a few years now, and my boss recently joined. During last week's session, he approached me and we chatted about work and music (which is totally fine with me) but then he suggested we meet this weekend and exercise together.
We have different goals, and I prefer to lift alone so I can do whatever I want (I lift pretty heavy and follow a custom routine)... And he is known for getting upset with colleagues over personal conflicts.
I enjoy working with my boss, but I'm not sure I could relax with him outside of work. Additionally, I'd prefer not to use short term avoidance as the solution. So how can I keep the business and personal separate without it affecting our work relationship?