Ok, so I went out on my 4th date with this Spanish chick. 1st date went out to a ton of bars and brought her home. 2nd date went to a movie and dinner and she didn’t come back b/c we both had to get up early (but she gave me like 6 kisses before leaving the cab). 3rd date was a disaster, she went through my phone (nuff said), and was crying, then got her back to my place and she left again, then begged to sleep over, gave her my roommate’s bed, then she came into my bed, apologized and we slept together.

4th date went to a sex museum with oysters and wine. Then went to a rooftop bar, when we got in the cab to go back to my place. This was the convo

Her “so where are we going”
Me “back to my place”
Her “what are we going to do there”
Me “probably just go to sleep, maybe you can change out of those clothes”
Her to the driver “Actually, can you drop me off here….bye”

WTF?

In my opinion, she got scared. Judging from what you said you, kinda made your intentions clear on having sex with her which made really uncomfortable and she thought that she need to get hell out of there. Not only that you mentioned the 3rd date was a disaster. If it was that much of a disaster then what ever you did on that date and after may have been part of the reason on why she wanted to leave.

That's my take on the whole situation.