Optimistic philosophy to thwarted love

Its raining outside...its a pleasant Saturday evening..I am wondering how come I cannot spend this romantic evening with someone special. As I lay thinking, I noticed the soft copy of a poetry that I had downloaded from the internet the other day. I read the poem again and a thought crossed my mind. Why is the failure of love celebrated as the most perfect instances of love?
I realized that unreciprocated/thwarted love is central to the romantic visions carved in many poems and novels. Goethe in The Sorrows of the Young Werther paints a beautiful vision of love, love as a feeling. Love according to this view is a sequence of special and intense emotions.
Werther is continually longing for his beloved:
“‘I shall see her today,' I exclaim with delight when I rise in the morning, and look out with gladness of heart at the bright, beautiful sun. 'I shall see her today' and then I have no further wish to form; all- all is included in that one thought."
He is exited by her contact:
" How many heart beats when by accident I touch her finger, or my feet meet hers under the table! I draw back as from a furnace, but a secret force impels me forward again. Sometimes when we are talking she lays her hand upon mine and in the eagerness of conversation comes closer to me and her balmy breath reaches my lips,- when I feel as if lightning had struck me and that I should sink into the earth."
He is Doubtful:
“I watched Charlotte's eyes, they wandered from one to another but they did not light on me- on me who stood there motionless, and who saw nothing but her. Her carriage drove off and my eyes filled with tears. I looked after her; suddenly I saw Charlotte's bonnet leaning out of the window and she turned to look- was it at me? Perhaps she turned to look at me. Perhaps."
He values love and its beauties:
“What is the world to our hearts without love? What is a magic lantern without light?"
Essentially these 4 intense experiences: Longing, Rapture, Doubt and the fact that he is in touch with the source of all value defines the vision of love. However when he meets her she is already engaged and emotionally attached.Werther eventually kills himself as he has no possibility of bringing his love to fruition. His longings are never converted to satiety. He is desperate to see her but never finds out how it would be to see her every day. He is exited with the touch of her feet essentially since he feels they were not supposed to touch. I wonder if the intensity would remain if he could touch her whenever he wanted to?
Similarly in the highly acclaimed story of Romeo and Juliet, we find an instance of love for the same reasons. Death after a single night prevents the couple from having to sustain their passions. They cannot be bored or have to confront any difference in opinion.
Coming back to the poem which initiated the thought. Its a Robert Browning special called 'Porphyria's Lover'. The poem is about a lover who wanted to make his love eternal, kills his beloved the moment he realizes that she worships him. It begins with a picture of heavy storm and rains which could implicitly imply the trials and sorrows which the lover is going through in his life and how his beloved shuts the coldness and the storm in his life with her presence.
"The rain set early in tonight,
The sullen wind was soon awake,
It tore the elm-tops down for spite,
And did its worst to vex the lake:
I listened with heart fit to break.
When glided in Porphyria; straight
She shut the cold out and the storm"

This is followed by a beautiful and romantic description of how Porphyria tries to convince her lover of her affections for him. She put his arms round her waist, made her smooth white shoulder bare, made him lay his cheeks there and proclaims her unconditional love. The lover realizes that she has submitted herself to him and is proud of the fact that she worships him.

"Murmuring how she loved me — she
Too weak, for all her heart's endeavour,
To set its struggling passion free
From pride, and vainer ties dissever,
And give herself to me forever."

The lover wonders how he can make this moment of romance an eternal moment as he debates with himself. And then he finds a thing which he can do. He strangles her with her hair.

"That moment she was mine, mine, fair,
Perfectly pure and good: I found
A thing to do, and all her hair
In one long yellow string
l wound Three times her little throat around,
And strangled her."
The lover is convinced that she has not felt any pain and as he kisses her cheeks now he feels assured that he has gained her love for eternity. He claims that even God has approved of his act.

"And thus we sit together now,
And all night long we have not stirred,
And yet God has not said aword!"

Yet again a failure of love is seen as a beautiful instance of love. I have not been able to convince myself on this philosophy. Hope i can get some explanation soon.