[quote=@harinezumikouken]
<Snipped quote by Lucius Cypher>

Agh, you unfair fuck. You know Shiro's character can't just walk away after something like that! Damn you. DAMN YOU TO HELL! -Shakes fist at sky-

But, okay.
[/quote]

Gren only wants Shiro to trust him to let Gren's help him. But before he can do that, Gren's also needs to show Shiro that Gren's trusts him too. And he showed this to Abel because he has faith that Abel is a good guy, and that he might have some baggage that needs fixing too.