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There's one relationship milestone that is so obvious we often mark it with a celebration, and that's time, whether you're planning a big date to marvel over your one-year anniversary or still in shock such an amazing man uttered the words "I love you" three years ago.

But while time is ticking away, proving your commitment to each other, additional, less obvious milestones are happening—some we may not even recognize! So whether you've stood the test of time or you're still tentatively dipping your toes into love's waters, here are eight sure ways to tell you're serious about each other.

1. You realize you can't go a day without talking. My guy admitted he knew he was falling hard when it felt weird we went a day without texting or talking. When you're serious about someone, that person occupies space in your day that feels odd or empty when he or she isn't around to fill it. You crave that daily connection, even if it's nothing more than a simple "good morning" message.

2. He volunteers to sit through your favorite TV dramas, and you've jotted the return of Game of Thrones on your calendar. When he's caught up on each and every teenage love triangle and you're willing to give up a Sunday night for gratuitous gore—or whatever he's into and you're not!—you know you're both on your way to having it bad.

3. You're Facebook friends with each other's BFFs. Making your relationship Facebook official is an obvious step into the land of "It's Getting Serious." A more subtle, but equally significant, sign is when your mutual friend count soars from zero to 10 because both sets of friends have given their online blessing.

4. He buys you a toothbrush to keep at his place. "I knew it was serious when my boyfriend made casual mention I didn't have to pack a toothbrush or my favorite face wash to stay at his place," says a friend. "He bought both and tucked them into his medicine cabinet so it would be easier for me to stay at his place." You don't have to purchase and stock each other's favorite bathroom products, though that's a very nice gesture—getting serious looks like a trail of your better half's toothbrushes and nighttime necessities at your apartment.

5. You've got keys to each other's apartments. When my boyfriend copied his keys for me, it was out of necessity: I needed to be able to come and go from the apartment as he worked during my weekday visit. When he told me to keep them after my trip ended, it was, I like to think, a gesture that showed he trusts me. Andwithout trust, you can't get serious.

6. His friends are comfortable hanging at your place. Getting together as a group is cool, but when you're inclined to host a group of boys at your house—and they want to have drinks at your place rather than the bar—you're in, and your guy is smitten with more than your cocktail recipes.

7. You've fallen into the "we" habit. When a friend asks you to a party, you respond, "we'll be there." When a work crisis hits, he tells you, "we'll figure it out." And when you talk about where you'll take your next vacation, it's all about where "we are going to go." Moving from an "I" to a "we" is serious stuff, people.

8. You're meeting each other's parents. Better yet, you have met them, and it went famously. Because when you're serious about someone, wrapping that person seamlessly into your family is uber-important—you not only want your siblings to marvel over your awesome catch and garner your parents' approval, but you want to see that he or she could have a permanent, welcome place at the table.