Hey man, don't let the game get to you, after all it's not really there for anything more than to entertain you. If you don't feel fulfilled, or if you feel as if you haven't accomplished anything (though you surely have) don't worry about it, pretty much everyone in this game is gonna feel that way sooner or later. Pretty much I think things more or less are along the lines of this general trend for the average gamer.
Start out with hopes and dreams, thinking of all the great stuff you're going to do, and then you finally go out and do almost all of it as you're going through the game. You meet alot of people that you come to call your friends, and you connect with alot of people. But in all of that, you find yourself a little disappoint. Why is it that this happens? I don't know, why is it you still feel this frustrated urge to do something about it? Because you aren't satisfied with how much you've accomplished. The goals that you have met are very lofty indeed and you should be proud of what you've done.
I can tell you one thing, after you beat the game fully it'll probably leave you with an empty feeling of, "Ok. . . now what do I do?" but you know what, it's just a game. These things happen. You get so sucked into it that you don't realize it will have an end, or will come to an end eventually. All you can do is brace yourself, and look back on all the good times you've had, and move on with things.
I agree with some of the other posters, take some time off, and go do things with your life. I know you'll feel a little better about it.
Sorry to see you down Jim, even though I haven't really talked with you all that much in game, I still think you're a cool guy. Anyone who can actually feel emotion in this game, and see the reality behind it deserves my sentiment. Hope things look up for you soon. Send a tell if ya wanna talk.

You're on my friend list for a reason you know.