I wonder, by my troth, what thou and I Did, till we loved? (1-2)
His current love is so life-changing that the speaker can't imagine how he lived without it. The "by my troth," an old way of intensifying what comes after, making it clear that this is partly hyperbole. Of course, they did things before finding each other. But the deeper, sweeter point remains: [cue Andrew Lloyd Webber] "yes, love, love changes everything."
For love, all love of other sights controls,And makes one little room an everywhere (10-11)
It's a small poem but it makes a big claim: erotic love is the most powerful kind of love. Why? It's obsessive and consuming, turning your attention away from everything else and focusing it on a single person. As a result, that one person becomes a substitute for everything else and your shared love creates its own universe.
Let us possess one world, each hath one, and is one (14)
Nothing makes you more exciting, beautiful, brave, devilishly sexy, and endlessly entertaining as being in love. Once you're loved enough, you become like an alternate (and way better) reality to your lover. You're family, Facebook, Chipotle, and summer evenings on the beach all wrapped up in one.