I'm beat. 我好累. I'm bushed. 我很累. I'm exhausted. 我累死了. I need to go home. 我必须回家. I need to get back. 我必须回去. I can't stay. 我不能留下来. I have things to do. 我有事情要做. I have to go. 我得走了. Let's call it a day. 我们今天到此为止.
