There is a massive difference between love and sex. Using my current relationship for example. When i first met my girlfriend i argued with her over the amount of change i received in a shop. Later on in the month we both came to the same party where we got talking. At this point i thought she was a nice girl but i didn't really have much of an interest.
After a few meetings, i was walking her home when i realised i didn't have my keys with me and i was locked out of my house. She suggested that i just come in and stay at hers. After much thought i took up the offer. We had sex for the first time that night, and it quickly became a sex buddy relationship.
It wasn't until we were having sex that i realised the difference in her. She was so attractive to me all of a sudden, i put it down to the fact that it was because she and I were always at it together. But over time i just couldn't help but fall in love with her.
We're happy together now, and we love the way it all fell together.
The difference here is that it is two completely different emotions, controlled by two different areas in the brain. Its quite easy to hate someone but still lust with sexual desire.
If you ask me though, personally, i would prefer if sex came before love. As i confuse lust with love easily, after lust is taken out of the equation through sex, i can then see how much i really do like the person. Don't get me wrong, i do actually have to like them before sleeping with them though!