You can have love and lust separately, or they can occur together. Lust is a biological state; it's your brain responding to hormones that your body is creating. Lust is what drives the desire for sexual relations.
Love is a psychological state. It is created in the brain, though it affects the body as well. Love is usually tolerant and long-lasting, whereas lust is a temporary state and is purely physical. Sometimes lust leads to love, but more often not.
A short way to say is it that lust is in your body, love is in your mind.