I'd imagine...

[He runs a hand through his hair, glancing aside and not looking entirely convinced.]

...L-look, this is some pretty heavy stuff...

[He can't imagine what he'd be like if his own brother suddenly vanished on him. ...Oh wait, no...he can at least take a guess.]

...If you need somebody to talk to or just to pass some time with give my Terminal a ring, okay?

[He's not going to press the teenager about this, but he also doesn't want Donnie to try and deal with this alone.]