Having sex while a child is in the next room

My fiance and I are TTC #1. My ex's eight year old little boy lives with me at the moment. According to this app I am in my fertile window. We usually only have sex when the child is visiting his grandparents, but I don't want miss out on the opportunity to get pregnant. I didn't plan on the child living with me when I moved in so I only have a one bedroom apartment. I don't know if it's okay to have sex with the child here... advise please!