Certainly, the list of best love poems & quotes should start with Khalil Gibran’s poem:

Love One Another

Love one another, but make not a bond of love
Let it rather be a moving sea between the shores of your souls.

Fill each other's cup, but drink not from one cup.
Give one another of your bread, but eat not from the same loaf.

Sing and dance together and be joyous,
but let each one of you be alone,
Even as the strings of a lute are alone
though they quiver with the same music.

Give your hearts, but not into each other's keeping,
For only the hand of Life can contain your hearts.

And stand together yet not too near together,
For the pillars of the temple stand apart,
And the oak tree and the cypress grow not in each other's shadow.

Let These be Your Desires

Love has no other desire but to fulfill itself
But if your love and must needs have desires,
Let these be your desires:
To melt and be like a running brook
That sings its melody to the night.
To know the pain of too much tenderness.
To be wounded by your own understanding of love;
And to bleed willingly and joyfully.
To wake at dawn with a winged heart
And give thanks for another day of loving;

To rest at the noon hour and meditate love's ecstasy;
To return home at eventide with gratitude;
And then to sleep with a prayer
For the beloved in your heart
And a song of praise upon your lips.
----
What is the world of literature without Shakespeare?
Here is the poem which is quoted so many times quoted in movies,
when Gibran’s poems of love are more often directed to ‘how to love’,
Shakespeare more than often talks about the loyalty of love
between two souls. 

A trait I long to master.

Sonnet 116
Let me not to the marriage of true minds
Admit impediments. Love is not love
Which alters when it alteration finds,
Or bends with the remover to remove:
O no! it is an ever-fixed mark
That looks on tempests and is never shaken;
It is the star to every wand'ring bark,
Whose worth's unknown, although his height be taken.
Love's not time's fool, though rosy lips and cheeks
Within his bending sickle's compass come;
Love alters not with his brief hours and weeks,
But bears it out even to the edge of doom:
If this be error and upon me proved,
I never writ, nor no man ever loved.
---

The next one is Love’s Philosopy by P.Shelley.
Remember that by nature, by whatever greater power you believe,
 everything seen and unseen came in a pair.

The fountains mingle with the river,
And the rivers with the ocean;

The winds of heaven mix forever
With a sweet emotion;

Nothing in the world is single;

All things by a law divine
In another's being mingle--

Why not I with thine?

See, the mountains kiss high heaven,
And the waves clasp one another;

No sister flower could be forgiven
If it disdained its brother;
And the sunlight clasps the earth,
And the moonbeams kiss the sea;--

What are all these kissings worth,

If thou kiss not me?

~ by dhanio on November 21, 2007.