Ordinarily I would say that placing yourself in the company of someone who has done this to you would be folly, and whether or not it is victim blaming, it is still true that if someone treats you bad and you go back, then it gives their warped mind permission to keep doing it because they are thinking you deserve that and more, because they are f*cked up. I don't consider that to be victim blaming either, it's just stating that the way these types think, you cannot be around them and if you choose to be, then bad things will most likely happen, so it's best to not give them the opportunity to do what comes naturally to them, as psychos. No one is to blame for the warped perceptions and actions of dicks like this except the dick, and he's not about to self-reflect, so it's best to avoid their company.
Given the fact that you say you blacked out entirely from the drug, and did not recall it even happening, so the next time Sam invited you somewhere, or got you to drive him somewhere, it seemed ok, and you were still best friends and everything was ok. That's how you felt at the time, suppressed memories tucked safely away. You are definitely NOT to blame for this in any way whatsoever, and I hope you can allow that message to absorb in your mind, as you read everyone's posts here.
If you can treat yourself as kindly as possible at this time, it will help preserve your strength for getting through this. I hope you have other people in your off line life who can give you the support you deserve and need at this time. And of course, we are all here to listen if you need an ear or a hundred :)
Can I just express how utterly scary this world is becoming, or has it always been this way? I'm pretty sure, not. When sub-humans like this little f*cker can get away with rape using date rape drugs, on someone who considered them a friend, and introduce their friends, basically pimping the girl out to his mates...then this is not a society I want to live in, or at least, hurry up and get all those freaks who want to start again on Mars, to go, and take these creatures with you.