**結んでゆく is sort of a flirty double meaning, as it's literally "connecting/bearing fruit/linking up then go". It's like saying "how bout we hook up then come?" to somebody in English... has that sexually charged naughty double meaning.
**永遠 is usually "eien" for eternity, but she's going with "towa" 永久, which is something more abstract. They mean the same, and the prior kanji are fine, just note that she sings and means the abstract eternity "towa" despite seeing the common one.

Another romantic song by Yagami-chan. It has a really good funk, the feels of being at a party, meeting someone you feel like you've known forever, making love, celebrating, but having this bridge of reality nudging you that it's just for the night, but you want to ignore it and keep it going.