Ever, forever and always
Those three words have similar meanings, but what is the difference between them and what are they used for? Thanks!

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I can't do better than this http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv352.shtml
It's very comprehensive

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"Ever" is usually used in question form in the Present Perfect.For example
"Have you ever visited Spain?"
For ever means "until the end of time" for example. "I will love you for ever".
And this is similar to "always" .We can say "I will always love you", like in the song "Bodyguard". But we use "always" in the present simple too, to speak about habits.For example 
"He always drinks his coffee with no sugar". It is not talking about what will happen in the future, but something we do habitually, or every day.

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'Forever' means for an infinite length of time.
'Always' means at all times.
'Ever' is a question word (and is also used in negative sentences); it has no time value.