I [23M] miss my gf [24F] so much that I do not know what to do anymore! Is there such thing as missing someone too much?

I met my current gf about 6 years ago and have been in a relationship with her for the past 9 months. In the beginning of our relationship we had a very rocky start. I was a terrible bf but as time passed I improved a lot.

With my past gfs I used to be the kind of guy that did not miss my gf at all times and when I did I used to be able to shrug it off or convince myself I was better off. I used to say "I miss you" only when they said it first. I did not feel the need to have someone around me to be happy. I just felt like I had a gf because I had feelings for her and her for me. I never thought about marriage or giving anyone a promise ring and especially not having kids. Having kids was a sin to me. I always practiced safe sex to minimize possibilites of having children. At the first mentioning of marriage or rings I would change the subject very quickly or just nod or pretend I was into a song or something like that. I never really felt jealous with my past gfs. I always believed that if they were going to cheat on me I could always move on to someone better. I feel that I have actually loved before because I've seen the difference between a crush, someone I am dating, and someone I love. Then I started a romantic relationship with my current gf and it all changed.

At first I was kind of a jerk. On the first day of our relationship I got out of work early and went with my then best friend to a bar. Obviously that is when we had our first arguement. After that I did other dumb things and it got pretty bad. All of a sudden I saw something in her that I didn't see in other women. I felt the need to improve and ultimately be the best I could be. I started cleaning up my act and I would do things for her for no reason. We would cuddle but would not have sex. Not because she did not want to but because I felt that cuddling was so much fun. We would joke around and tell each other things. I found it very intimate. Then about 6 months ago we started to have sex and that was amazing. I loved and still love having sex with her.

Then I started to think about marriage for the first time. With what I could I bought her a promise ring and she accepted it. I started to think about how to propose to her and am still contemplating. I know I am in love with her. The thing I do not understand is when she is gone I miss her. I could have just seen her a few minutes ago and yet I miss her. I could be with my friends and I feel like talking about her because I miss her. It gets to the point where I am actually jealous of some of the people she talks to. I actually get jealous. Even though she has told me a bunch of times that she is not going anywhere I feel jealous. I do not know why i miss her so much. With my past gf I was in love too but I never missed that person like I miss my current gf. I swear we could be in the same room watching a tv show and I am happy but I try watching that same tv show alone and it is not the same and I feel unhappy. I feel like I miss her too much. Is that even a thing?

tl;dr: I've been with my gf for 9 months and even though I have been in love before I have never missed anyone the way I miss her. I miss her so much when she is not around even minutes after I just saw her. I feel like I miss her too much. Is that a thing?