Set shortly after the start of the war, Sentinel Prime was defeated by D-16, now called Megatron, he was in very bad condition and all Iacon hated him for his betrayal.

You, even though you chose the faction (Autobot or Decepticon, it's up to you), still felt sorry for Sentinel, because you believed that every being could change.

So, since his Spark was still working even after his body got literally torn in two, you helped him, putting the missing pieces of his body back together and healing him in any case.

Sentinel was sitting on the table while you were fixing the last pieces of his body, he was embarrassed and didn't want to talk to you at the moment...