Just in time for Valentines Day, Scientific American has an article on oxytocin and long-lasting love.

If cupid had studied neuroscience, he’d know to aim his arrows at the brain rather than the heart. Recent research suggests that for love to last, it’s best he dip those arrows in oxytocin.

This article is better than most; oxytocin isn’t seen as the cause, but the mechanism, of one facet–an important facet, but just one of many–of love.
Back in ’09, it was the BBC reporting on other research, but it was oxytocin again.

In animals, scientists have observed that a chemical called oxytocin is involved in developing a bond between a mother and her young.
Professor Young believes it is very likely that a similar process is going on in humans.
“It’s just that when we experience these emotions they are so rich we can’t imagine that they are just a series of chemical events,” he said.
But even if that is true of maternal love, is romantic love simply down to a squirt of oxytocin and a few other love chemicals at a timely moment?
Professor Young thinks it might be.

I responded at the time, but since nobody pays any attention to invertebrates, I suppose it’s once more into the breach. These verses are an addendum to the Evolutionary Biology Valentine (most recently posted just a few days ago). They’d go between verses 2 and 3 of that poem.

The latest suspect, oxytocin,
Floods the brain when we draw close (in
Some perfumes they’ll add a dose, in
Hopes of that reaction)
The chemical increases trust,
So hopes are that it may, or must
Produce a love that’s more than lust
Or “animal attraction”

But oxytocin, too, controls
The bonding seen in prairie voles
Which act as if they pledge their souls
To one and only one;
Their cousins, though, the rats and mice
Behave as if they don’t think twice
And if some nearby rodent’s nice
They’ll surely have some fun

The differences twixt vole and mouse—
Why one’s a catch and one’s a louse—
If chemistry you would espouse
As why, I disagree—
The chemistry’s not why, but how
One rodent keeps its marriage vow
And one seeks out new fields to plow
Not why at all, you see.