Do you feel consumed by emotion?
Are you passionate about him? Have you started and then stopped yourself from sending him little emails? When you’re with him, do those emotions intensify? Do you have to work hard to seem calm and collected when your mind is racing? Are you experiencing mood swings, from happiness to sadness, many of which are dependent on the attention you’re getting or not getting from him?

Are you eating? Are you sleeping?
Often when we start to like someone, we feel a sense of exhilaration, a tremendous sense of energy. Our hearts race, and we forget to eat and have trouble sleeping.

Are you changing yourself?
Whether it’s your clothes, your hair, your taste in music and movies, or even your priorities and values, when we start to like some we often emulate them and change ourselves in ways that we think will make us more appealing and attractive to that person.

Do you want exclusivity from him?
If he was just a hook-up, it shouldn’t matter if he sleeps with other women. When we don’t really like someone, we don’t care if they see other people. It’s only when we start to like someone that we want or even demand exclusivity.