Yes, Brandon's first time was with Cheryl. The episode is, after all, called "The First Time". And I agree with those who say he didn't sleep with Emily until college, so he must have only slept with Cheryl at this point. I mean, doesn't it make perfect sense that of course HE would take such a condescending, arrogant attitude towards poor virginal Ahhndrea when he's barely not a virgin himself? ASS. HOLE.
(which reminds me, Tara, you teased about the Brandon Challenge but then never actually did it!)
Side note: I was a little disappointed- no snickering over David's comment that Donna doesn't need to worry because neither of them "have any diseases." Sure, no diseases...YET!! Give yourself time, young Silver.