Need some help...

I want to be in a relationship. I so want it. But i am creating an issue for myself. When i start liking or dating a person, I start getting possessive for him. I start expecting. I expect he will call me. I expect he will reply to my message. I try my level best to hide it, but it comes out. I start getting anxious and nervous.Most of you guys might think im completely normal. Yes i am.. Its ok to expect, i know.. But why i start overthinking so much? It really affects my ability to work and make logical decisions.And possibly, i start thinking that the guy did not like me and he was talking to me because i was talking to him.I know i am asking a very common and a predefined template kind of question But i need some answers, even if they are answers which i already know...