Why did the Jews forgive ukrainians the pogrom in Lvov?

It was a Polish city at the time.   

Why not? Hate corrodes the soul of the hater more than it hurts the hated one.  Who wants a corroded soul?

Besides, as another person here pointed out, the rapists and their victims are dead. The blood guilt is ended on earth. The haters have their judgment from God. 

It is right to remember and be horrified, so that we will fight against hate; but if you pile hate atop hate, then you do nothing but hate. And it is not sensible to gate the dead.

First, it was the Russians, not the Ukrainians. Ukrainians themselves were oppressed, persecuted, and genocided by Russians under the Soviet regime of Stalin. Second, any Ukrainians that may have been involved are dead or on the verge of dead because they'd have to be pushing 100 years old at least by now.