Pay Dirt Photo illustration by Slate. Photo by Getty Images Plus. Pay Dirt is Slate’s money advice column. Have a question? Send it to Kristin and Ilyce here . (It’s anonymous!) Dear Pay Dirt, I need advice on how to handle money with my friend group. There are four of us who hang regularly, two are a couple who recently bought a house (we’re all in our early 20s, for context). Because they have the house, they’re the default hosts, and because they host, they often end up paying for things like food and covering things like entry tickets for logistical convenience. Except then they turn around and say not to worry about it when I offer to pay them back for those things, which makes me uncomfortable. There are a few reasons for this, but the main one is the aforementioned house. They told me how much their mortgage is, and I know roughly how much the pair make. The (admittedly back of the napkin) math doesn’t totally math.…