I don't think he's realizing that he's never going to have the chance to apologize. That's not very Steve, because he's a soldier. He understands sometimes you don't get to make things right with people who don't come back from war. And that's what that moment is. It was a battle, and he understands that not everyone makes it out alive, but he never expected Tony to be that someone.
In all honesty, I think Irene is the only woman who could actually handle Sherlock. Mycroft can barely deal with him and he's Sherlock's brother, Molly doesn't stand a chance, Jim was way too unstable, and John... Well John is special because he's John Watson. Every Sherlock in every incarnation needs his Watson. But Irene really got to him. She took everything he threw at her in stride right up until the very end. That's what makes her character stand out in my opinion.
Aw man, I don't want to think about Tony missing Steve so much that he's sitting in his room. My poor sweet Iron Baby! He tries, with every beat of his heart, to do the right thing. And it always backfires on him. Stop hurting Tony, he deserves to be happy!