There was a chance he was letting himself get overly stressed about this situation, but there was good reason. There could be a consequence for everything he had to say, a wall put up between them while he desperately tries to regain a rapport with her over the truth.
How would she react over the fact that they had an intimate relationship and she left him for Oliver? How would she react when he told her that barely year later she left Oliver due t the fact that he was hiding things from her? Or Havenrock, or Laurel?
"Diggle's one of the best men I've ever met, but we were never that close. You three, Oliver, Diggle, and you, make an amazing team." Which makes her being here all the more tragic.
He also just looks at his sandwich, trying to figure out what to say next. It was nice to hear a story like that, but everything on his mind had to do with her and his relationship to her.
"I think we should talk." Specifically about their relationship.
He sits down at the table as well, as he'd been leaning at the counter.
"Not sure how to start but I feel like you deserve to know."