I'm not that good at formulating responses on the internet, and I'm also an amateur Slavic Historian, but I will try my best. :)

During the birth of the Soviet Union, many of the nations within the Russian Empire began wars for Independence, Ukraine was one of them. The Soviet were in a war with the Ukrainian freedom fighters. Both the Soviet and Polish were actually fighting to keep Ukrainians down because they both owned Ukrainian land and wanted, desperately, to keep it. Poland saw that the Soviets were having trouble so they invaded Ukrainian lands to try to expand eastward, as they feared Germany (which owned them until the end of WW1) would want to take land back, so Poland wished to grow bigger.

Poland succeeded to a degree, and they took Ukrainian land from the Soviet, because Soviets were fighting independence wars on all fronts. Since the end of the Polish Soviet war in 1920, some Ukrainian nationalists were bitter, of course, and outraged that the Poles took their land so arrogantly. The Soviets were also outraged, and always wished to get the land back. The Soviet Union signed the Molotov-Ribbentrop Pact which split Poland down the middle (complete simplification), with Ukrainian, Byelorussian, Lithuanian land going to Soviets and Polish, German land going to Germans.

Of course now everyone knows that the Germans betrayed the non-aggression pact later and invaded Soviet land, this led to an uprising with partisans. Guerrilla fighters which wish to hurt Germans in any way possible. Some would kill Slavs that worked for the Germans, others would destroy train tracks, some would just kill Germans. However, in Ukraine, the Bandera partisans had a large focus of murdering the Poles. Some historians think that was their only focus actually, to remove Poles from what once was Ukrainian lands. The Banderas succeeded, and with them came severe and horrendous massacres of Poles.

Everything I've read about Stepan Bandera was something along the lines that he hated the Poles for taking the lands, however he did not simply want to massacre all of them, only the intelligentsia (which is still of course horrible). I read somewhere that he wasn't the one who made the choices to massacre people though, I know he was in a concentration camp for a large percentage of World War 2, so I don't know if he could've made those choices.

That's a little background (I really don't know how well I put that all, so sorry if it sucks). He is loved by Ukrainians because he wanted to free Ukrainians, he hated Russians and Pollacks because they both took Ukrainian lands and people and took advantage of them, and he was right in a sense. It is true that he is loved by a lot of Ukrainian but he is also hated by a lot of Ukrainians, my whole family hates the Bandera's and they said they when they lived in Western Soviet Ukraine, people influenced by him would come around threatening the Jews in the villages. He is both hated and loved throughout Ukraine the same way many other famous nationalists are hated and loved throughout the world. People like Malcolm X, Gandhi, Nelson Mandela, except Bandera and his groups had more of a mean streak, putting it lightly.

I hope this was informative, this is actually my first post on Reddit.