How do you forget someone easily that is still constantly in your life?

the guy I'd been friends with and crushed on for years recently rejected me...and unfortunately this school year we have 3 classes together, so I see him every day...

how do I forget? how can I detach myself without seeming mean?
I thought I moved on over the summer cause I had 2 months without him, but sometimes I get sad and I want to talk to him again but I purposefully blocked him on social media so we wouldn't talk and I would stop hoping for something that won't come...is there a way?

I want to be friends again but I'm scared that I won't be able to trust him (and he knows) especially we tried a few weeks after the first semester started, and he said he'd try again...but he wasn't really putting effort so I didn't understand what the point of being friends was...

I'm just so ... so confused y'know?