"Earlier, you told me you were in a physical relationship with a guy named Adam, why didn't you sleep with him?"
Although Steve was weirdly happy with the fact that Erica didn't sleep with this guy, he wanted to know the reason behind it.
Erica wanted to face-palm herself as she brought this Adam topic the night before.
The reason she never slept with Adam was because, although she was making out with him, she kept thinking about Steve.
Erica felt it would be unfair to her and to Adam, also she could never bring herself to share the most intimate feeling with anyone else but only with someone she would wholeheartedly love.
Erica was waiting to fall out of love with Steve and fall in love with someone else.
Six years passed by and she couldn't and unexpectedly things between her and Steve progressed till here.
The want in Erica which was ignited the night before, transpired to the current situation.