Sisters are not people who know each others' deepest, darkest secrets. They don't always hug and laugh and cry with each other. They're not always each others' shopping buddies and some don't have nicknames for each other. Sure, some sisters may act like this, but these things aren't part of the dictionary-definition of 'sister'. Indeed, sisters are just strangers thrown together by fate at a very young age who happen to have some of the same DNA strands in their bodies. We fight, we hate, we ignore, and if we're lucky, we learn to live with each other in quasi-peace.

When someone comes into your house who is not related to you and is just your sister's friend, you tend to be on your best behaviour; you hide the ugly sides of relationships. However, when that person moves into your house and your sister moves out, you're stuck with someone who believes that in reality, sisters act like the people in those feel-good family movies. That person doesn't know who is hidden behind the nice smile and the cheeky – yet good humoured – remarks. No, she just believes that you are the perfect little sister who she can adopt – like one would adopt a cute puppy. Because when someone adopts a puppy they aren't thinking of chewed-up underwear and pee-stained carpets; they're thinking of velvety ears and family Christmas photos featuring a sweater-wearing dog.

But you know what? It's time for my house-mate to open her eyes and realize that I am not her best friend, her 24/7 shopping buddy, her shrink, her wedding planner, or her exercise partner. I am not her sister. Can you smell that, dear? Its the stink of pee on your Persian rug.