>>279903522
That was a side-goal. In Fate and HF routes he's fine with Shirou, but calls him retarded.
In UBW, Rin kept dragging Archer face-to-face with Shirou's idiocy and he got disgusted. He then decided to kill Shirou and try to make him give up on his ideal to validate his cynical view that he gained on it during his time as Counter Guardian.
He has no choice but to be summoned. He didn't go back in time on purpose to kill himself.