1. I cannot but stay with him.
2. I cannot help staying with him.
3. I cannot choose but stay with him.
4. I have no choice but to stay with him.
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Are they all grammatical. I know 'help' means 'avoid.' Then what does 'but' mean in #3 and #4? Does 'but' mean 'except'?
2 and 4 are best.
1 and 3 are very awkward. I've never heard anyone use those sentences' phrasing before.