You can go, but I _____.
You can go, but I _____.
Explanation
"must" implies a strong necessity or obligation on the part of the speaker.
The sentence would be "You can go, but I must stay," indicating that the speaker is obligated to stay.
"must" implies a strong necessity or obligation on the part of the speaker.
The sentence would be "You can go, but I must stay," indicating that the speaker is obligated to stay.