I'll just chime in (still deferring to Sohee) and say that itsumo is more like
always in the sense of "all the time, all day long, on a consistent basis" as opposed to
forever, which is better translated as itsumademo or eien ni (although that's more poetic, like "eternally.") Zutto can also be used as always or forever or just "the entire time." These words are kind of confusing in English too actually so some of what I wrote is probably wrong.
So I'm thinking along the lines of maybe, All day and all night, it's love/ Lovin' you all the time, something like that. I'm pretty bad at translations.