Joey's 'lie' was telling Bendy that he would be adored or become human. No wonder he squashed Sammy - he thought Sammy had destroyed his other half! If Bendy was created from footage of Henry - the names are even similar, after all - then he may be trying to merge with him in order to stabilize himself, similar to what Alice Angel is doing with the innards of a legion of Boris-es. Koko was rotoscoped from footage of Max Fleischer's brother, Dave Fleischer, in a clown suit.

Coupling this with the WMG further down the page about needing a connection to someone raises another reason why Bendy is after Henry, as well.

If the beginning of Bendy's life (who seems to have also been created by a life-recreating animation machine for, as far as we can tell, just because Joey could) was anything like Koko's, things probably got real dark, real fast. Max Fleischer's early work, meant to show off his invention of the 'Rotoscope', an animation machine that would help give animation more fluid, life-like movement, consisted of him literally at one point emptying an entire inkwell trying to pull out his character, a clumsy but artistic clown, who had jumped into it in an attempt to escape him after spending a good portion of the episode being insulted, ignored, having things thrown at him, and then chased. I watched the animations just to see what they were talking about, and the connections between 'Bendy and the Ink Machine' and Max Fleischer's 'Out of the Inkwell' were pretty startling.

I have to second the above Troper's theory.Bonus points if Henry just stood by and let it happen, whether he felt bad or not. Koko may have had his moments of mischievousness, but treating a sentient being in such a way is cruel and unusual, so it isn't too far-fetched that Bendy was experiencing similar treatment and wanted to end it once and for all. Things Max has done to Koko include shocking him with electricity, setting his paper world on fire as 'thanks' for rolling Max a cigarette, drawing Koko onto a very steep mountain with a small area to stand on to 'keep him quiet for the night,' and cramming Koko back into the small cramped inkwell solely because Max had a nightmare about him. He was mistreated a lot in these shorts by his creator, Max Fleischer.

Bendy wants revenge because he was mistreated by Joey.Fleischer Studios, the company that created Betty Boop, had a series of shorts called 'Out of the Inkwell' wherein a character named Koko the Clown interacts with the real world.

Bendy and the ink machine chapter 5 ost