The first thing I'd do if I were you would be to evaluate why it is that you cry until he returns. I'd call that a fairly serious problem, because it indicates that you aren't capable of being alone for any reasonable amount of time. And since the odds are fairly great that this relationship will one day end, you really need to be able to develop an ability to enjoy time by yourself for just such an eventuality.
What are your hobbies? Any outside interests? Do you have many friends? Do you do any sports? Have a job? Anything else to occupy your time? I'd find something and start doing it...nothing is worse than sitting at home feeling glum while your mate is out and about. By the time your mate comes back home, you're in a foul mood and that tends to spread rather rapidly.
This is one of those things that is far easier said than done, but I think you've already identified some of the problems you are having...and that's a solid first step. You know that you need to calm down a bit with your reactions, and you know you need to be happier with him not around. Both of those are things you are going to have to do consciously, and the only thing I can tell you from personal experience is that such things do change over time. I think as I grew older and matured a bit, I found myself less likely to blow up over small things and more likely to enjoy my alone time almost as much as I enjoyed spending time with my partner. I have a feeling this will change over time for you as well...my first relationship was filled with a lot of the things you are describing, and nowadays they're basically all gone for good.
Alone time and "together" time aren't better or worse than one another...they're just different. There are things you can do alone that you may not necessarily be able to do (or want to do) with your mate. My partner doesn't like all of the things I enjoy, so I do them when she's away. When we're together, I do things that we enjoy doing as a team and it keeps both of us happy. The key is finding things to fill in both categories. Activities you and your boyfriend both like can fall under the "together time" slot, while activities you enjoy doing by yourself would come during your alone time. Sound pretty intuitive?
I think there is a bit more going on here than you are letting on, at least explicitly. You did mention that he is good at telling you he cares about you, but not so great at showing it. I think this is at the root of your problems, and nothing outside of a good ol' fashioned talk can solve that problem for you. You're going to have to sit down and mention this, perhaps come up with ideas of how that can be changed, and see what happens. I'm willing to bet he might have some things to say about that too, which could benefit you by letting you know what areas you can improve in.
You'll never know until you have that talk, and I'd do it as soon as possible just to get things straightened out. Sound reasonable to you? I hope it all works out...good luck!
BruinDan, "Number Three," PHOM
Beware the naked man who offereth you his pants.