When you say "that one guy" or "that thing from eighth grade", she knows you're talking about the guy who took you on a horrible date to McDonald's sophomore year or the time you got pantsed in gym class.

3. You never have to watch what you say or how you act around her.

She's seen it all from you over the years--mean, grouchy, angry, devastated, stressed, overexcited, underwhelmed, crying, screaming, laughing. She's seen you act a million different ways and still loves you. There's no problem being 100% honest and real with her about what you think and how you feel.

4. You never have to worry about entertaining her when you're together.

Over the course of nearly two decades, you've taken more naps together than you can count. You have plenty of fun memories, but you're comfortable just chilling on the couch together watching Dance Moms and eating junk food. You have all the same favorite movies and shows anyways, and being together is better than being apart.

5. You never have to wonder if she's being honest with you.

You'd know if she was lying anyways, but she knows that having your back sometimes means telling you that the guy you're dating isn't good enough for you or shooting down the idea that you could rock the fanny pack trend.

6. You never have to go through anything alone.

After all this time, she's got a sixth sense about your feelings. She knows immediately when you need her and goes above and beyond the call of duty to make sure you feel loved and appreciated and taken care of, because that's how much she cares about you.

7. You never have to apologize for being you.

She knows everything about you, even the weird stuff that usually freaks other people out. But at this point, she could care less that you sleep with socks on or that you sometimes eat leftover lasagna for breakfast. She accepts you and loves you, quirks and all.

8. You never have to worry about constantly maintaining your relationship.

You've got your awesome life, and she's got her awesome life. As time has gone by, you've met new people and had experiences separate from each other. Sometimes, that means losing touch for a little while. But no matter what, you're always able to pick up right where you left off, and nothing ever changes.

9. You never have to wonder if someone is rooting for you.

Your best friend is your number one fan. When something good happens to you, she's the first person to text you, congratulate you, or plan a surprise celebration. She would never view you as competition because your successes are her successes. She's proud of you no matter what, and loves nothing more than to see you happy.

10. You never have to wonder if you'll always be friends.

Your friendship has stood the test of time, and there's not much that would ever come between the two of you. Your best friend is your soulmate and your other half, and you'll never let her go. You can't anyways. That girl knows too much.