So you've been seeing your partner for a while now and you've been missing them a lot lately...now you're wondering why you're missing him when a few hours pass by?
Well the most likely answer is that you are becoming emotionally attached to them...your feelings do get stronger over time and this happens when you are especially close to each other and tend to share almost everything.
So when you are away from your partner there feels like a piece of you either emotionally or physically is missing, almost like you are missing your other half...am I right? This is the kind of emotional attachment that is caused by the chemicals that get released when we begin to fall in love. There is one particular chemical that creates a euphoric, elated and attached feeling that draws you in...it's called dopamine. This would explain the feelings that you are going through both physical and psychological. This could also be a big part of the reason that you may get a little worried when your partner isn't around and you may feel like you are missing out on something...or even get a little concerned that they are around other people.
I wouldn't say this is because you are a jealous person but rather you feel like you should be taking up most of your partners time and if you aren't then you are missing out on something. When you end up in a relationship a sense of ownership is almost granted to both parties and this feeling can get stronger with time, it's the same feeling you would get with a dog or cat. If you don't give your dog or cat enough attention or they give more attention to someone else you may feel left out or vice versa.
This is a natural human reaction when you are emotionally attached to someone...so don't freak out you aren't going crazy...just make sure you react to it all naturally and don't turn into a crazy person!