I think I'm kind of stuck st around the same points as the person above me.
I have no clue what to do with Lisa. I ended up with Olivia as my girlfriend, Alex is out of the picture. Whenever Olivia comes over Lisa joins us, but nothing to hardcore. IIRC she's not interested in Alex anymore and I can't talk to her about anything. The threesome scene is always the same, so I can't progress any further that way.
The last thing I could do to Lisa in the Mentor quest was to buy her the sim card.
I've recently got rid of Eric, not sure if it has anything to do with it. The 'Mentor' opportunity isn't done yet, it mentions 'Classmate', which I don't even have yet (but Schoolmate - are these the same?).
What do? Any help is appreciated.