They didn't show Severide and and Erin sleep together, but it was implied, I think.
I watch both shows and, really, they're pretty much the same show. They're both Dick Wolf productions with a lot of the same producers, same location, same overall feel. I don't understand liking one and not the other. One's in a firehouse, the other's in a police station. That's the only major difference I can see. Even the cast - at least several of them - were on CF before the spin-off happened.
I question the sensitivity of the bombing storyline, especially coming so close to the Boston Marathon bombing anniversary. Not that NO show can ever have a bombing storyline ever again, but one involving a race AND close to the anniversary.....it just felt like a bad decision. I'm sure the shows will be good, but I think they could have accomplished the same thing with another plot device causing the trauma.