Is it normal to regret and not be able to forget him?

4 years ago i used to like guy and he used to like me too, we never talked but everybody told me he liked me and it was obvious he did cuz he always stared at me. i was so shy back then and couldnt get along easily with guys . he tried to get close to me by knowing my friends but i was really unapproachable and never showed any interest . years passed and now he has a gf, he's had her for several years. in the beggining of his relationship with her he could be talking to her and stare at me but he has been with her for many years now and i dont see him any longer, sometimes by chance but i juts dont look at him. i just regret that i didnt give him a chance back then as i was so young , shy and unexperienced. i wish things could go back and i would be approachable. is it normal to remember him until now and is it normal to regret or should i move on and just forget?