1) Library boy scene - to trigger this you need to get to a point where your need to study more...
2) Butt "plugging" with Lola (if you choose to let Lola help Lily...)
3) Butt "plugging" at the hotel (If you didn't let Lola help Lily)
3) Working as maid at the hotel (2 branches)
4) Getting "help" from Fred
There are a few non sex scenes as well to build up before the sex scenes but they will come naturally when you play.