It wasn't meant to be.
They drifted apart after returning to Earth, amicable but going separate ways. Don's led to Penny.
Today's their first anniversary.
Mother feared she'd be angry about the engagement, but even if she was, the wedding's joy cancelled it out; the tears she held back didn't lament but revel.
Being in attendance of the joining of two she loves most—her sister and a man she's happy to call a brother—was delightful. The cherished memory lives on.
Together, they glow. Anyone can tell they really are in love.
And that's all she needs to know.