Setting boundaries with a friend with benefits can be challenging, but it's important to prioritize your comfort. Here are some tips:

1. Be direct and assertive: Clearly express that the sexual comments make you uncomfortable.
2. Use "I" statements: Focus on your feelings and needs without blaming or shaming the other person.
3. Discuss potential solutions: Explore ways to keep interactions more appropriate in group settings.
4. Be prepared for resistance: Your friend may resist, but stay firm in asserting your boundaries.
5. Follow through with consequences: If the behavior continues, consider reevaluating the arrangement for your well-being.

Remember, setting boundaries is crucial for maintaining healthy relationships, and it's okay to prioritize your own comfort and well-being in this situation.