I often find myself fantasizing about having a girlfriend or wife and that we have a wonderful relationship. But it doesn't really help make this a reality since I am not going out and meeting potentially great women but rather lying in bed day dreaming. Still, I think it is better to have healthy daydreams (about good things) than all of the negative fantasies I have involving sex and fake intimacy.
I can't help but feel that I'm an escapist. I find myself always wishing that my life was more exciting, that it was more like a sci-fi or fantasy tv show, or a video game, that I was doing something that was really important, and that people really depended on me, and that I really mattered. I just feel like I'm not doing anything meaningful in my life sometimes, and I just feel like I don't really matter.
This is great that you bring this up because it shows that you have passion for life, but that you are not sure what exactly you are supposed to be doing. My advice is to try some new things and see what excites you. It might not be something physically invigorating like racing cars, or being an astronaut but it might be being successful at a reputable job: teaching children, helping older people, making customers' days, building and fixing things for people, serving your town or community, providing a quality service etc. are all important things that need to be done.
I personally believe God has important work for all of us, that we are on earth because we matter. People mistakenly think that only priests or ministers are serving God or that only doctors and scientist are doing "important" work. Anybody who treats others with respect, helps someone in need, and contributes to the well being of mankind is important, regardless of their occupation.
For example: there's this guy in my SAA meeting who did some awful things, was a total sex addict, who has no wife or children, no job, and who spent a lot of time in jail. He could have declared himself worthless and killed himself, or just spent the rest his life alone in his apartment. Instead, he comes to meetings every week and inspires everyone else to keep coming back and work the program. This guy is far from perfect, but he matters a lot to me. To be able to call him up any time when I feel triggered and get help is a wonderful gift from God.
So if this guy can make a positive difference, then the rest of us can.