'Tony Abbott, you don't know how to love your sister.'

Since the day she was born 22 years ago, my sister Lola has known how to love with all her heart.

She loved me when she was still a little grinning pile of pop-art leggings and wispy baby hair, giggling as I blew raspberries on her tummy. She loved me when she was a little naked-bottomed sprite, galloping across a beach toward me.

She loved me as a rashie-clad, primary-aged sandcastle-builder, though I was a distant and moody teenager.

Lola has always wholeheartedly loved other people, too. She loved our Nanna, when her hearing, sight and memory went. She loved the children with autism she looked after in her part-time job. She loved my parents, through their divorce and re-partnering.

Lola’s love was deep and simply communicated. She was always the cheerleader of our accomplishments, the first one to cheerily place her hand on ours, and the one to curl up like a puppy on our laps during movie time.

And when she grew older, Lola loved a girl.

Lola didn’t make her relationship public at first, because she knew that saying it out loud would make the reality of sexuality official. She intuited that the world would not treat her as softly and kindly as she treated others.

But when Lola finally did say she’d met someone — and that the someone was a girl — I hugged and high-fived her. Her girlfriend came to family dinner the next week. The globe kept spinning, the only difference being the gentle glow Lola developed as she blossomed into who she was always supposed to be.

I couldn’t have been prouder of the person she’d become.

It was only when an acquaintance of mine asked, “Is the family… okay with her coming out?” that I realised some siblings aren’t ‘okay’. That, by virtue of being straight, some siblings think they have the right to pass judgment on a core part of their brother or sister’s identity.

Sydney woman Christine Forster has one such sibling.

Christine is engaged to a woman called Virginia Edwards, but her brother Tony Abbott does not want them to get married. In fact, Mr Abbott has told the entire country he does not believe his sister’s relationship is worthy of legalisation in the same way his own, straight marriage is.

Tony Abbott has used his position as Prime Minister to block a conscience vote on the issue, then to threaten to demote any frontbencher who defies him.

In his role as most powerful man in the country, Tony Abbott has also described his sister’s wish to marry as “the fashion of the moment,” suggesting that while he’ll attend their wedding, he does not really believe it will be a valid union.

Related: These are the people blocking marriage equality in Australia.

Tony Abbott’s words are not meaningless. They have a far-reaching legal impact for millions of Australians.

Crucially, they also discount his sister’s experience and identity. Those words must sting deeply and unforgivably, in the way that only a slight by your own flesh and blood can sting.

“Of course I’m disappointed in my brother, it’s a personal issue,” Christine said during a recent interview with Mamamia’s sister site Debrief Daily. “It’s linked with personal family relationships… This has an immediate and personal impact.”

Despite continuing to discriminate against his own sister, the Prime Minister somehow manages to sleep at night. He seemingly rests easy beside his state-sanctioned partner, the weight of his gold wedding band securely hugging his finger.

How comfortable that unquestioned privilege feels for all of us who never had to give a second thought before revealing who we love.

Related: Straight white men: You’re not oppressed.

When I lay down to sleep last night though, my thoughts turned to some images of my loving little sister:

Lola’s soft, freckled hand finding its place upon her partner’s at my wedding dinner.

Lola’s grinning, pretty face as she gave a reading at my wedding, knowing my nuptials are the closest she’ll get to a marriage ceremony of her own.

Lola’s expression of weary acceptance when the news broke about the government blocking a conscience vote this week.

That face carried a story that broke my heart: That she’s so used to being treated as a second-class citizen, the government’s bigoted actions don’t even surprise her any more.

I love my sister, and I wish for her a country that allows her to celebrate her relationship in the way I celebrated mine.

Tony Abbott must think he loves his sister, too. But if he truly believes her relationship is not as valid as his, that his own family member is not worthy of the same rights, that there is something unnatural about his sibling’s very identity?

Then he does not truly know how to love.

I’m sure that somewhere, Tony Abbott feels a deep sadness that his words damage and discriminate against the first girl he ever cared about: His sister Christine.

I’m sure that sometimes, he wonders if he’s doing the right thing — not only as a leader, but as a brother.

The marriage equality debate is about love.

It’s time that Tony Abbott showed some.

Related content:

Penny Wong on marriage equality.

To the Liberals who will defy the PM over marriage equality: Thank you.

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