He was willing to trust her, quite literally, with his life. She had been indirectly right the first time she tried to guess what he had to tell her. There could only be one reason Clark would go that far - he loved her. Telling her his secret was far more binding than any declaration of love. Telling her meant he saw them together forever
I liked the parts everyone else liked(especially when the bad guy gets beat up), but this line really said SO MUCH about how wonderful a thoughtful, contemplative Lois can be, that this conclusion about whether he loved her or not was best explained by him revealing his secret. Just Awesome!
TEEEEEJ
