If i have a girlfr right now this is what i'll tell her :

I can't promise the future, but there are things i'm sure of right now. I can't promise you won't shed a tears, but i can promise to make you laugh when you cry. I can't promise bad things won't happen, but i can promise to be by your side through the bad times. I can't promise you won't be hurt, but i can promise to fill you with sweetness to mend the wounds. I can't promise to be there in your whole life, but right now i can promise that i'll be there for you.