alright, route attempted! i didn't get the success ending, but here's some tips:
1) try to encounter him in the forest at night. you don't have to go there, it'll be prompted when you go to sleep. just go to history as usual.
2) stack up on strength. you'll need moderate strength to choose an option that guaranteeds the good ending.
3) if sal isn't in class, then skip it. find him somewhere else.
4) remember to go to fields during curricular activity (queensguard) to unlock sal's cg!
5) basically just to talk to him as much as possible. do your best!