Hello Ippodamo, welcome to Using English!
I would guess that your question relates to the song by Oasis; in which case, "live forever" is a fragment of the phrase "You and I are gonna live forever", i.e. an infinitive + adverb.
In terms of translation, on the other hand, perhaps the title should reflect your version of the full phrase "are going to live forever". (If that is likely to involve an ordinary future tense, perhaps the adverb would suffice.)
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