The Words "I Love You"...

The words "I Love You" you hear them so often spoken. Perhaps you say I love you to your dogs, your cats, your horses? Perhaps you say them to close friends or family members?
Why is it those words, when spoken by the right person, can cause you to feel euphoric? You feel like floating away on a cloud. They give you fufillment. They give you a sense of security. They fill a void in your heart and your life.
Love is one of the most basic instincts of the human nature. So why is it, that sometimes we are afraid to show love to the ones we love the most? Why is it we are selfish in that way? Its something I dont understand, but yet I myself am guilty of doing it.
I never thought the words "I love you" could impact me in such ways ever again. I mean after all, I had closed off my heart to experiencing that dreaded emotion and had been quite successful at it for 2 years.
However, that afternoon in August, as I leaned up to attack his neck with a kiss as i moved to his ear, I felt him lean close into my body, and place his mouth next to my ear. Fully expecting to hear him say something totally stupid to ruin the moment, or have him lick my ear, i braced myself. He moves even closer and I hear a whisper "I love you". For a moment, i stopped breathing, my eyes had teared up, and I couldnt get words out. I leaned in close to him, kissed his neck and made sure i got close to his ear too. I managed to chokingly whisper "I love you too Chris." and suddenly lost all urge to kiss him and just laid my head on his chest and listen to his heartbeat. Something I had done ever since we met. He wouldnt let go of me this time when his arms wrapped instinctively around me. Instead, he pulled me as close to him as i could possibly get without becoming apart of him.
Those words have rebuilt me.
But why is it I am still so scared of them? So scared, I know I dont say "I love you" as often as I should or as often as I'd like to (thankfully he knows I love him, by everything i do) and he is the same way, although I often question whether or not he loves me. LOL.
Those words fufilled me, they gave me security..they give that to me even now, even with our future in limbo.
I just wish they came out easier..