It absolutely gets better. It will be difficult to fill that void, but it can be done.
Personally, as an IV heroin user my life was completely consumed with myself. When I began to live with compassion for the first time in years, when I began to see what help I could provide the people around me rather than just worrying about me; things got a lot better. It gave me a sense of purpose and eventually allowed me the experience and opportunity to help other people struggling with addiction. At this point, no offense OP, but you probably haven't got a ton to offer the world. Start small. Volunteer at an animal shelter. Go to a soup kitchen. Help Habitat for Humanity build a house for someone.
As my life's trajectory changed, my self esteem has recovered. If I feel that void beginning to establish itself within me today I know what I need to do: rededicate myself to something besides me. I never realized what a selfish mess I was. I'm definitely not perfect now, but changing my approach has helped me to minimize the feeling you're having--I almost never feel that way at all anymore. I am certain you can get past this awful feeling, just don't give up. You have two dogs inside you: a compassionate and loving one and a selfish self-loathing one. The one you feed is the one that will grow.