Is this sentence OK? I would have been happier,if you had stayed home.
I thnik there is a better way too say this,but I don't know how.

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Answer

It's correct. As the two people above said, the only wrong is that you don't need a comma because the position of "if" is in the middle. But if it comes at the beginning of a sentence, you will need to put a comma(just like this sentence).

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The sentence is fine - except you don't need tie comma after "happier."

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It sounds fine to me. Your friend came out with you last night, but you had such a miserable time together that you wish that he or she had stayed home.
Other than the spacing/ punctuation, I can't see a problem with your sentence.

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