1

So this is a line from the anime Oregairu. From what I know, I would say ある and あり mean the same thing. However, I could be wrong so is there any special reason why 'ari' was used first and 'aru' was used second in this sentence?

2

青春とは噓であり、悪である is a single sentence.

The first あり is an example of using the masu-stem as a connector similar to the te-form. See also this and this answer.

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