I might be a scumbag friend.
1. Friend's Sister while 5 people slept in the room
2. Different Friend's Ex-Girlfriend
3. Different Friend's Actual Girlfriend she asked for a ride home from a party, not my fault she thought my truck was powered by blowjobs apparently. Things escalated quickly.
I'm not even sure if those were the first 3. There was a period of about 12 years of blacked out drunk that started when I was 14 years old.
Meh, first two are kosher. Maybe not the best stuff to build a friendship off of, but kosher. 3rd is kinda... I mean it takes two to tango, so she's got partial blame, but... yeah you should have declined and told your friend. Although if one or both of you were drunk things might be a little more understandable; and she clearly wasn't a loyal GF. So you're not that bad.
And this is from a guy who partially defines himself by his loyalty to his GF and friends. Judging from this post you may have been more opportunistic than I would have been, but you didn't seek it out; and that counts for a decent bit. I define "scumbag friends" as those that intentionally abuse your friendship. You're more "normal" than "scumbag".