Sure, everyone has their good friends and even their best friends. But when you're lucky enough to find your 'person' (or if you're lucky and have more than one, your 'people'), you cross a boundary and basically acquire another sibling. If you and your best friend meet the following criteria, you two can basically consider yourself siblings.

1. No conversation topic is off limits.

You and your best friend will openly discuss everything from something as mild as your school work to all the gory details of your romantic relationships to any and every health issue you may have. You two have no boundaries.

2. You're perfectly comfortable seeing each other in your underwear or naked.

You two are way past the stage of trying to look presentable around one another, so naturally, comfort comes first. You'll hang out together in your underwear with no makeup without thinking twice about it. You also more than likely change together frequently and don't think anything of it.

3. You don't withhold your bodily functions around one another.

Burping, farting, or anything of this kind is no longer gross to you two, so naturally, you let it fly freely.

4. You frequently insult each other.

You always know it's out of love and just joking around, but you and your best friend can insult each other with the best of them.

5. You simply cannot imagine ever living without them.

The joy of having a sibling is a built-in friend. You and your best friend have crossed the line from friends to family, which means you'll both always be there for each other throughout life, no matter what. This isn't just a convenient for the time and place friendship; this is your friendship soulmate, and that lasts forever.