Have you bought all of the items related to him and seen those scenes? Prior to the route split/school closing, most of Liam's scenes require that it be a weekend to trigger due to his work+Cody but after that the requirements should relax a bit.
Dreamscapes from 4-5 require that you are already on his route and have seen certain events beforehand.
You can check the guide for more concrete requirements.
I hope this helps!