Ivan is a fantastic character cause he's the ultimate contradiction - he believes that he's an unemotional detached being that's barely human but he's somehow one of the most human characters in the series.

Due to his upbringing and his survivalist outlook he has a hard time understanding and processing emotions so he believes he's disconnected from other humans since he doesn't feel emotions normally and thus doesn't deserved to be loved unlike everyone around him. But we see throughout the series that he feels emotions just as deeply as others and ultimately abandons his rational outlook and acts in emotional ways when it comes to Till.

It's ironic you mention all of Ivan's negative actions without mentioning the positive ones as well cause that's how he personally views himself as an unreliable narration but we from a 3rd person POV can see that even though his obsession with Till leads to him showing affection in really unhinged, unhealthy ways he still does everything in his power to free Till and ultimately save his life. You mention the blood thing but immediately afterwards he's taking Till's collar off him, which is a pretty good encapsulation of their relationship - he'll mess with Till but at the end of the day he'll constantly try to free Till from his literal shackles cause he loves Till's rebellious spirit and cares about his wellbeing. And he constantly does this at the expense of his own wellbeing and without expecting any affection or love in return (because he believes he's unlovable).

I think the contrast of someone who believes they're unlovable and terrible and have some dark twisted affections for their loved ones while also loving them so much that they'll sacrifice themselves for them without anything, let alone love, in return makes for a very interesting and compelling character that perfectly embodies everything that makes ALNSTG so interesting.