There are plenty of options that press themselves forward for consideration.
As the most romantic phrase we could ever utter to someone.
I will never leave you.
I feel utterly seen by you.
You are incomparably beautiful.
But we may need to go down another, more surprising, sterner route to really honour the enquiry.
If we define romantic in an effective sense, meaning helpful to the survival and enhancement of love, then we may need a very different approach.
We may need a sentence like, if you ever stop being nice to me, I will leave you in short order.
It may sound brutal on first reading bitter paranoid, a bit jumpy, far from what we imagine romantic to mean.
There must be a mistake.
But with a few ghastly experiences behind us, we'll know that this is precisely what we may need to say in a kindly but confident voice if the qualities on display in the sweet opening moments of love tenderness kindness consideration thoughtfulness, politeness are not to give way in time to scratchiness irritability, neglect and infidelity.
It's a bitter truth that other people treat us more or less exactly in line with the way we imply that we can bear to be treated.
Lovers sense one another's limits and will push relentlessly forward until they reach them.
If we send out signals that we will reluctantly but passively take mystery, take unfair accusations, take a lack of effort, take cancelled plans and take the constant intrusions of a gang of mean-minded friends.
Then, cruelly, this is precisely what we will end up having to deal with.
Our furniture will be scratched, our fridge emptied, our patients exhausted.
The human animal, in all its perversity and sinfulness subtly, intuitively adjusts to precisely the expectations placed upon it by its partners.
We do as much as, and not a jot more, than we're called upon to do.
We'll do manners when manners have been insisted upon and we'll do casual, impudent disrespect when they haven't.
We'll do apologies when these have been set as the price of peace, and otherwise we'll sulk and throw blame around.
As teachers with impeccably behaved classrooms have long known, the audience adjusts itself to whatever expectations have been defined.
Those who signal big consequences seldom have to meet them out.
Surprisingly, though such intentions may sound harsh, no one especially minds.
They may even feel immensely grateful and more loved.
It can be profoundly reassuring to be in the presence of people who promise to protect us against our own sloppiness, who restrain our temptations to decadence, who are on the side of our more exigent hopes for ourselves.
No child actually likes an adult who will let them do anything.
And nor does a lover.
Half the population have known all this in their bones from the start.
The wisdom began on the first day of school.
Don't let them mess around with you for a moment.
If they touch a hair on you, they won't know what hit them.
Those who are protected by other people grow into native experts at protecting themselves.
But the rest of us, the ones who may have wasted a decade or two in shenanigans with sweet-faced monsters, we need to learn the lessons the hard way.
From waking up in appalled wonder after our bank account has been emptied or our partner vanishes with someone they had an affair with online.
Those with a bad childhood must suffer twice.
The first time in the childhood itself.
The second from the expectations of ill-treatment that they silently bring to bear upon their adult relationships.
The next time we begin a love story, we must be immensely kind, of course.
We must listen, we must invite them out, we must remember special occasions and send sensitive messages, but we must also defend ourselves with a lion's strength against their and our own temptations to cruelty.
We will only make love truly flourish by insisting very tenderly, very early on, that we will simply tolerate nothing else.