OUCH

Nobody deserves on something like that. Go to prison? Yes. Being betraying, cheating, lying and manipulating by your loves one, who you trust, help and about who you care? No
Nobody deserves to hear from his lover that you are most important for him, that he would die for you and next day discover that he cheating you with your enemy, betraying you and everything what he told you was big lie and manipulation.
Specially that Yanek saved him, helps him, cares about him, was tender and good for him. He even risks his life for him.
Diesel is awfull like person, he has only look. Bigest disappointment.

You are that one girl that likes the douchebag and shield him with her life until he mistreats you and ruin your life. Get yourself together, please.

Yanek is a cruel manipulative jerk that took a thraumatized kid and molded into something useful to him without caring of what Diesel was going through.
Yes, this is because Yanek is a thraumatized kid aswell. He lives in shadows and blood because of his father so that's the only thing He can give to others; we can understand that... but He is still a toxic and terrible person. You NEED to understand that.

What you need to understand too is that Diesel is a victim in this whole thing. The psychological pressure in his shoulders is more than whoever can handle. Even if I don't condone cheating He has a lot of good reasons to act like that.
You really need to start thinking about how Yanek impact negatively Diesel's life.

I'm tired of explain that even if we like a person or character, that doesn't mean He is a good guy. Or if someone hurts a character that we like he is not automatically a bad person. The real world doesn't work like that, dear.