ANSWERS PLEASE: Is it wrong to still think about your former crush?

I used to text my crush all the time about life and stuff like that. And I remember sitting next to him on the bus and feeling this really strong spark between us. I think he did like me a little bit, but I liked him a lot. But that was then. We eventually parted from each other and didn't really speak only because I felt like I was doing all the work and he seemed to not really care at all for me when I trying to form a friendship. I texted him early this summer and asked how his summer was going, but then he stopped texting. I only texted him early this summer because he kept appearing in my dreams. Now summer is almost over and he's reappearing in my dreams. For some reason he always seems to be in my mind and dreams again. Right now he's taken. However, after we parted I dated someone else and I did get over my former crush. It just started up again. I don't know why I keep thinking about him. Help?? I need some advicee! 10 points!!