I actually feel the opposite, we've missed one of the biggest clues the mangaka has dropped which is Truck-kun always comes for someone in despair. Sensei already said Truck-kun ruined the happiest moment of his life which means Sacchan was in despair. Perhaps that her love with him was to brief or that she decided she wasn't ready for death? Remains to be seen but I feel like the proper ending is her finding peace with the reality she and Sensei aren't a perfect match no matter how hard she tries to fit the empty hole in his heart...although knowing this is leaning towards harem it might just be her along with the priestess and tama trying to fill in his heart but somehow that seems like a bad end where he hasn't changed he's just being kept by others for their own selfish desires.
