Wanting space after a long day isn’t rejection. Say it out loud so they don’t guess wrong.

Needing an hour alone after a long day is about the day, not about the person in front of you. The difficulty is that silence is easy to misread, so what was tiredness gets received as coldness and then there are two problems. A sentence prevents the whole thing. Saying it out loud costs almost nothing and saves an evening.

Try naming it as you come in: I need half an hour and then I am good. Give a time, because an open-ended withdrawal is the part that worries people. And do come back at the end of it, which is what makes the sentence trustworthy.