Try this
- Identify regular hours and any preparation or travel involved. Check which existing shared plans are affected.
- Discuss those changes directly and avoid assigning support tasks to the other person without asking.
A worked example
“I’ll volunteer on the first Saturday morning each month. I can still join lunch, but I won’t be free for our usual shopping trip.”
An invented example to adapt, not a real exchange or a script you have to follow.
Before you leave it here
The new activity can matter to one person without becoming a joint project. Ask separately before requesting transport, donations or attendance.