It's hard to conceptualise self-sacrifice as a selfish act because you usually don't come back so nobody ever blames you.
Especially the US are very big on the hero worship and you can't tell anybody their son/husband/brother/father was a selfish dick. Especially since that's a military or police thing for the most part.
And if you grow up being told that sacrificing yourself for others is just about the most noble thing to do, it's really hard to see that hole you are leaving. And Steven had the bad form to survive and come back unharmed, allowing Connie to be angry at him because he sidelined her when it counted, disrespected her conviction and then acted like it's no big deal. From his perspective he pulled the best possible outcome and saved everyone (except Lars, but he kinda got himself into it and he's alive again so it's all cool).
For Connie, Steven disrespected her love and resolve. She wanted to fight with him, but he just shoved her away and went it alone.
And he never felt the loss of his own sacrifice like that. He knew everyone was safe and he did the right thing. Scary, sure. But he's the big hero.