It means that the thought about you and what you guys had they missed seeing you and hearing you!
It's a good thing!
It could mean they really miss you, but from my experience I would say they are saying it to make you feel good. It doesn't mean they don't miss you, but typically a guy will think he is too cool to be whining about missing you all the time. Overall though I would look it as a positive thing - he either really misses you, or is thinking enough about your feelings to try and make you happy.
Hmmmmm...idk maybe they MISS YOU lol. It depends on the relationship you two have.
It means just that: I-miss-you. Why do you girls have to be so complicated? :-)