"It is worth something." He knows she could have just as easily not said anything and skipped the apology altogether. Steve would have justified a romance between those two forever even if logically in the wake of Ultron they're not even remotely compatible. Natasha stayed and Bruce ran. If that doesn't outline the difference between the two nothing else will.

He reaches out to take her hand. It's probably not the wisest move since he was just touching butter cookies, but it's not like he cares. "I value your trust. I intend to be deserving of it." He hopes she returns the favor. He can't justify having her around if she uses tactics like that on her team.