To be honest, they are quite similar. However, you cannot use them interchangeably in the past tense! Eg. He always ate a lot: Correct He forever ate a lot: Incorrect Always is usually used when the person can control the time limit but would like to continue until the end of time. Forever has a feeling that the speaker cannot decide. To be honest, except for the past tense, I think you can use them interchangeably (i.e. you can use forever instead of always and vice versa and it doesn't matter). Hope this helps!

Forever is longer because it has 7 letters. (Yeah, I hate jokes like that too, but I couldn't help myself. The other guy is right. They mean the same thing.)

Forever has no end result, no point of destination. Just moving and forever moving. Always will pop up forever, but there is no promise in the word; it's there for you, but it can go away. Then again you can always count on it to come back. I think always sounds more official; and forever sounds more romantic.

always and forever can be synonymous. "They will always love each other. The will love each other forever." However, when you're speaking of something that reoccurs from time to time, "always" can also mean "invariably": "When my car breaks down, I always call a tow truck." "always" can also mean "at any time": "If you don't like your job, you can always quit."

They're the same length.