Honestly, with many people mad at Ein for ruining a relationship, I'm pretty neutral. I understand why Yanek reacted the way he did with his trust issues and Diesel cheating with a cop, and I understand why Diesel "ruined" everything. He's a cop, he had to get Yanek anyway, and he didn't want Diesel to be brought down with him hence searching his background to send him home, being if he was kidnapped trafficked and ended up with Yanek, which was more than likely Ei'ns assumption with how he got to that Pastor guy, then he'd want to send him back to his family instead of getting tied up with this DANGEROUS guy. we can't forget that Yanek is a criminal. The only way I can see why Diesel would've cheated on Yanek, which I'm not justifying, I'm just giving a point to why in his mind he would've done it instead of what people think as he did it just to do it or it was forced, I think Diesel, being with the pastor and people alike for a long time, god knows how long, he stuck with Yanek because he didn't see him as a demon, and when Ein seemed to have accepted what he was and was still warm with him and even confessed he wouldn't kill him and wanted to send him away somewhere safe, Diesel might be attracted to what feels safe and warm because he was deprived of that for YEARS and dealt with drugging and r*e, nothing alike gentle and seemingly caring hands.