Nana has an open relationship with Shinichi and Mario.

Hello, and welcome to my den, where I describe my weird-ass dreams. Let us begin. In my dream I was back in college and the two middle characters in this image, Nana (auburn hair) and Shinichi (white hair), were dating. They were also my friends. I found out Shinichi was going to the local bar with his new start-up band and having some success. When Shinichi and I were walking back to the dorms after class he told me that Mario, the bar owner, had also started dating Nana and the three had an open relationship. I was carrying a box of pizza with me. Being the disgusting glutton that I always am in my dreams, I was obviously eating at the same time, straight from the box. While we took a break by the fountain and I engorged myself on more pizza, I saw that Mario had appeared and was talking to Shinichi who was taking a smoke break. I could overhear them talking. Mario said that he wasn't sure Shinichi was comfortable with an open relationship and because Mario was a gentlemen, he was willing to just break things off with Nana and walk away. However, Shinichi said that it's better when all three of them are in a relationship because he only has to hear half the nagging. There I was, pizza slice hanging from my mouth, as I watched them like a friggin' creeper. All I could think about is how I left my other pizza in the classroom. The end.

I understand Nana and Shin... they are both hos. But Mario? Is it because Peach cheated with Luigi?