Ivan is not a good friend to Till
I'm just going to preface, we're setting aside Till's own behavior for now and looking at how Ivan treats Till - or specifically mistreats Till, without any other caveats involved.
This is not hate or anti rhetoric. Do not use my posts to engage in discourse. I'm examining a specific facet of their relationship for a specific reason.
Beating up an already bruised Till
The artbook says Ivan has a strong fist from growing up in the slums, but Till just assumes he's a naturally strong fighter. Ivan can easily suppress Till, even when he's smaller than him.
Instead, he's having the time of his life adding to the bruises already on Till. A segyein teacher comments they keep fighting but concludes that's just how kids are. This means Ivan is repeatedly contributing to Till's bruises.
Later, Ivan grows up to be bigger than Till anyways. Ivan tells Till he wants to stop fighting: Till is smaller than him now so it's too much trouble to avoid injuring him worse than usual. Obviously this pisses Till off.
Till takes offence to Ivan suggesting he can't take him just because he's smaller now.
When Till receives a fixed restraint that restricts him even further, Ivan tugs on the leash and tells him "I told you so."
Ivan also calls him a loser when they're young. This is right after Till defined it as someone who is a friendless moron, and it clearly hurts his feelings.
Lets Till take the fall for him
In the Anakt Garden Kit, a segyein writes Till got into a fight with a new kid named Ivan and that fortunately Ivan has generously forgiven him. This implies Ivan didn't take any blame for his participation in it.
Ivan's behavior leads to Till getting blamed for things he didn't even do.
Steals Till's belongings and lies about having found them
In the Patreon, it's written that:
Ivan would steal Till's belongings just to return them later. He would pretend to be the one who found them, and this irritated Till very much.
He steals Till's pencil which Till needs if he wants to draw or compose. Ivan repeatedly steals the recorder Mizi gave him which Till calls his "one and only treasure."
Taking into account Till's guardian, the condition of his clothing, and his excitement at receiving gifts, we can infer he probably isn't given things often and probably doesn't own much to begin with.
Ivan steals his birthday gifts as well.
I'm told specifically Till finds the notion unsanitary. There's any number of reasons he could feel this way but Ivan doesn't let it go right away.
Till is already upset and on edge, and then Ivan prods at the exact reason he's distressed. It's also inflicting more pain on him, even if only slightly.
"A deep love-hate attachment"
A friend who is kind to you sometimes and mean to you others is not a good friend. That's obvious, isn't it? The acts of gentleness don't cancel out the acts of violence.
But Till doesn't see him as a friend. He sees him like a family member:
Someone you're stuck with no matter what. Someone who picks on you but has your back in thick and thin. Ivan confuses, irritates, and frustrates Till, but he also soothes and cares for him. He's someone who makes his life difficult, but he's also someone Till can fall back on.