[He likes Diana. She's smart, sexy, fun, and she's not Pepper. That means when he hurts her and she leaves, he won't be alone. He'll still have Pepper, the one person in this world he couldn't stand to lose. That's why when they all end up on the freezing cold beach after the skydiving date, Tony doesn't object when Natasha asserts that Diana and Erin are both he and Steve's girlfriends respectively. Technically, she's right. It's not a friends with benefits situation because of all the dates and he's been seeing her exclusively. He doesn't expect it to last. He wouldn't be here with her if it did. He wishes it was Pepper but it can't be. He just can't take the thought of losing her. He shoots Pepper a super quick text to see how business is, though.]