'Twere profanation of our joys
To tell the laity our love. (7-8)
Donne's speaker isn't just being a snob here, saying that commoners couldn't understand their love. He's saying that, if they broadcast all their heartache at separating, it would trivialize the joy they still share in their love.
But we, by a love so much refined […]
Care less eyes, lips and hands to miss. (17-20)
Like we said, for Donne, love is unstoppable. It certainly can't be held back simply by taking away physical presence.
Though I must go, endure not yet
A breach, but an expansion (22-23)
Love is powerful. It's also inexhaustible. Shakespeare said it in Romeo and Juliet: the more love you give away, the more you find you have. So when two true lovers part from one another, their love doesn't break in half, it expands.