I agree. While I can't deny that he feels somw thing for Yanek, I don't think that it is romantic love. I think Diesel is emotionally dependent on Yanek, who rescued him from "hell" and torture, but isn't in love with him. I see it more as an imprinting, where Yanek was the first one he associated with saftey, so he formed a deep emotional bond with him.
However, if they had all met under normal circumstances, I don't think Yanek wold have a chance because Diesel and Ein are clearly drawn to each other.
to me this fact you bring up was clear from the start.
and Yenak see him has a pet anyway and not a human with a will of it's own.
Just a humble opinion *pls. don't attack me for this* I think Diesel is with Yanek for the sake of 'protection' against anything and everything else (with him being a werewolf anf Yanek being the person that saved him from the church) and not the type of 'romantic love' that most people associate with. I think his just grateful to Yanek to the point that he literally gives his body to him in bed and his life as his personal guard. While he feels genuine attraction with Ein as evidenced with him always finding Ein's touches as gentle, plus that sexual tension they both have going in every damn chapter that they're together.