What is the difference?
Is lust a short-term emotion whereas passion lasts? Is passion more closely identified with love (or other strong emotions), and lust purely a sort of 'animal' need? If there is a difference, can one feel both at the same time, and would that individual notice the difference? Is it all contextual?
Maybe there is something a little grittier, more intense, and more instinctive about lust. I have a passion for faire, a lust for life, a passion for people, a lust for love, a passion for being, a lust for doing. So, maybe there is a difference there.
But, if we are discussing sex, (and why not?) maybe the difference is a difference of the heart. If lustful sex is sex that is pure animalistic instinct, a need being fulfilled, would that make the definition of passionate sex: lustful sex with someone you care about? And, if that were the case, wouldn't passionate sex be so much better than merely lustful sex? Wouldn't the passion only intensify the lust?
I think the bottom line is, I submit to passion… but, I am a slave to lust.