They occupied your mind. It may even feel like you have no control; you try to distract yourself, however you find your mind returning back to your point of contact. You obsess about what this person is doing, fantasize about what you would like this person to be doing or what your plans for the future may entail.
Let me tell you how fantasy can be very toxic for the love addict. My mom used to make this joke to me that “ I marry everyone I date”, meaning that by the time we get together, I've already picked out the wedding dress, the venue, where we are going to live and what our children will look like. The thing about obsessing and fantasizing about someone, is that often you create an image of this person that does not exist and you live this image in your head. When the person does not live up to the expectations, your codependency kicks in and now you find yourself needing to “control the outcome and the person”. Our minds are very powerful, they are like seeds.
When we nurture and feed them, they will grow. If we nurture and feed into unhealthy thoughts, they will also grow and determine your behaviors and emotions. When was the last time you married someone in your mind and how did that turn out?