Low-key mad can you get spam mail in your mail box??

My SO got a mail that was sent to his grandma's house. Well she said you got mail and it was in the back seat so I wanted to open it to see. Instead he kept saying let me see and putting his hand back so he can see before me opening it. Well he did and it said club something on the front. We have out own place with our address on our mail so im wondering why it was sent there. i told him what was it and let me read it but he didn't let me. So when we were in the store I tried getting it but he said stop so I just stopped but Every time we turned it's liked he kept looking back so I couldn't get it. Well he said I got to go to the restroom so I said let me read it and told him don't throw it away so I can read it at home. So he takes a few minutes longer than normal when he comes out I don't see it so I said you threw it away and he said yeah so I was like wtf seriously. So I said what was it and why he took longer he said he was trying to figure it out. So I asked what was it and he said idk it was some porno thing. He said I didn't want to tell you cuz then you would question it and get mad. So I got mad because what was there to hide from me and why didn't you let me read it. So it's like well I'm going to be madder because you didn't let me read it and now I'm curious on what it was. Is it possible to get spam mail or was it something he possibly ordered to his grandma's so I wouldn't get it and he could hide it? It just doesn't make sense why hide it and not let me see. Say I'm childish or whatever but idc. What could it been And why was he getting it. I'm already self conscious so it's not helping because now I feel ugly and fat. it's just suspicious and y'all might think porn is ok but I don't like it.