Sex

My boyfriend and I have been together for a year and a half. We love eachother and want to grow together and learn all we can about life. Someday we want a family, when we are ready. For a while now, I have caught him looking at porn, and hiding it from me. I tell him not to be ashamed, maybe we can watch it together. We have become very open with our feelings and desires. Until recently he told me he wanted us to have sex with other people, together. He acts like this a common thing for couples to do. I may know a couple people who do this, but for the most part, most couples I know don't. I am trying to be open because I love him, but think about this conversation all the time now and dont know how to handle it. Is this a normal thing for people to do and i'm just overly sensative? I feel i'm behind times, still wanting the life I wanted when we started dating, but i'm too old fashioned. I would be happy if we could keep or sex between our physical bodies. Any advice?