Severus noticed Lily's reaction, saw her close her eyes before she focussed on him again. He didn't need to be a mind-reader to know that Harry was still on her mind. One of the things he loved about Lily was her caring heart, meeting her future son was not something that was going to be forgotten.
"Any time with you is a good time." He stated simply, he knew that time would be limited because what ever her feelings for him were in this room was a boy that was Lily's future son.
Severus was not a nice person, he knew he would probably hold a grudge for the rest of his life when de day came that Potter stole Lily from him but he would always love Lily, he would always remember the time they had together. He would always remember that, at least for a while, she called him her boyfriend.
"Are you having a good time?" He might not be a nice person, Lily brought the best out of him, to her he could only be nice.