1. You’ve stopped worrying that they will run off the next morning without contacting you again. That fear you initially had of “when will they call?” after hanging out together has faded away. They always called and make it clear that they want to see you again.
2. You actually know their last name. Whether they have any siblings. What they do for a living. Where they grew up. They know the same about you. They know how you take your coffee and can order your favorite type of pizza to your door because they take time to learn these things about you. In short — they are no longer a stranger and feel like a friend. They know all about your crazy aunt Susan and the time you went streaking in college. It doesn’t scare them away.
3. You’ve had multiple conversations in a sober, daylight context. You’ve had numerous meals together and dates that don’t end with blacking out or drunken sex. They’ve seen you unshowered, sweaty (from working out, not from other physical activity), and in your sweats and find you more attractive than ever.
4. You’re not thinking about somebody else when you’re with this person. This is especially important if you recently got out of another relationship or are on a break from a former love interest to “test the waters.” You’re not comparing this person to your previous relationships and thinking that you wish they “could be a little more like ____.”
5. You find yourself thinking about this person when you’re with somebody else. Like out to lunch with friends. At a business meeting. Using public transportation. Or while hanging out with someone who used to interest you but now makes you realize why it never worked out. You’re excited to meet up with this person for plans because you know it’ll be fun even if you’re just watching TV together. You get a quick thrill when your phone buzzes with a cute text message from this person.
6. You’ve had “the talk” about your sexual histories, birth control, and how things will go down once you decide to green light things (i.e., condom, the pill or something else?). You’re not uncomfortable asking questions on this subject and can make it seem more interesting than a mutual medical interrogation.
7. You’ve kissed and done enough ground work to learn whether you want to proceed for more action. Like a bad appetizer warning you not to try the main course, you’re aware that a bad kisser can easily become a bad lover. Be open to discussing your likes and dislikes. Point out “no-fly” zones to avoid any distressing surprise behaviors.
8. You’re not having sex to keep the relationship or because “it’s expected” after a certain period of time together. Sex should be a happy accessory to an already blossoming relationship.
9. You’ve thought about how things will change afterwards and are prepared to deal with the consequences. This means potentially being exclusive, or having the talk to decide if that’s what you want. It also means being in a position to do the groundwork of being in a relationship. Sleeping together usually marks a point in the relationship where things either get serious or fizzle out. You should be prepared for things to go either way.
10. You trust them. This may be all you need. You know them enough to be confident in how they feel about you. So go for it. Or don’t. Only you know if you trust them. 
