Lust is a state which can be prior to love. It accompanies a sense of physical attraction but can be short-lived too. A person tends to like the body of the person without much understanding the mentality of the other person and expecting some specific things. Love goes beyond everything. In love, you accept the person as s/he is and try to attain a balance of your thoughts and principles and your partner's attitude towards them. But love cannot succeed if it is one-sided. It needs to be from both sides to continue in a lifelong relation.

Basic difference is acceptance. In lust you perceive your partner as what you want or hope to see. This seems to be a perfect projection of person rather than seeing a person in reality including his shortcomings and behavioral imperfections. In love you accept the whole person including his weaknesses. You can know that you are in love when you do not really want any changes in your partner's personality and behavior even being aware of flaws present there. In love you accept the person in totality and in lust you seek what you want in person and expect to change it if does not match your idealization. Love is a wonderful and rare feeling.