At the beginning of the song, the narrator is crying because he is so deeply in love with his beloved but she seems to be pulling away from him. We can guess this not only because of his tears, but because he says "this world turns cold" and, most significantly, "cause you're my ... true love ... please don't throw that away."
His beloved is threatening to walk away and he is desperately trying to convince her that he loves her beyond all measure and would do anything for her. He says he would even die for her:
I'll be there for you through it all
Even if saving you sends me to Heaven
He wants her to understand that he will not only die for her, but he also wants to be with her forever. He expresses the deep yearning of a person fully in the throes of romantic love, pouring himself out and expressing the fullness and sincerity of his love. He also shows love's abjection, as he is willing to be abused by her, as long as she stays with him:
Use me as you will
Pull my strings just for a thrill