Communication! You and your partner need to have better communication between you. Without a good communication, your partner doesn’t know your needs. The opposite is also true.
There is a misconception about rest time and autism. It doesn’t mean doing nothing or laying on the coach/bed. It’s often doing an energizing activity. I can’t give any clue here as the activity is personal and change from one to another. I can only speak for myself with trainspotting, walking in the nature, reading research papers…
It’s important to sit down and communicate about the needs of both with the partner. It makes things clear and people around us will understand why we are doing it. It’s also respecting the needs of both.
N.B: Now, communicating and respecting our needs is good. But, we can’t make up needs at one point to excuse ourselves. I see way too many autistics that have suddenly a new need to excuse being an assh*le. This isn’t fine.