That's not the interpretaion I got. She was fawning over him, yes, but that doesn't equate to "I want to fuck him." Trust me, I've had a number of girls treat me in the same fashion, and just because a girl fawns over you doesn't mean she's gonna take even so much as a single step in the direction of a relationship with you. Aeris was just more more vocal about her affection for Cloud than Tifa was. She didn't make any serious advances, she was just flirting with him.