Knowing.

 I know my love for you is my love alone, but your love gives my life meaning. I will never get you to love me, but I am happy to know he makes you feel the way you make me feel. I know you will be happy together. I bless the marriage, but I curse knowing I am too late. I will watch you marry him, I will tell you I am happy for you, (I am) and I will live on forever knowing.