Someone very wise said 'the only constant in life is change.' That applies to every aspect of life, including and especially relationships. Does is hurt to move on? You bet. Is there life after a break up? You bet.
There are no easy answers, nor are there any shortcuts. You grieve for the relationship you once had. Grief hurts. Allow yourself to feel the loss and the pain. Allow it, but don't lose yourself to it. You get to shape your life into whatever dream you choose. So explore those dreams even as you cry those tears. No crystal balls here. Only you and your thoughts, only you and your feelings, only you and all the things you hope your life will be. Let your heart heal. Then brush off the dust and get out there and enjoy the world. No predictions on life being better, only the reminder that life is for living. And like any storm that comes into your world, this too shall pass.How to move on from a 3 year, serious relationship? without going into depression!?
Keep focusing on your future. The past will creep up on you, but you have to keep facing forward. Do you want to be with this guy forever? Do you want to marry him? Think of how much better you could do. Think of how you're going to be happy with someone who's better for you that you can trust and enjoy and won't act like such a jerk. One day, you're going to be with the perfect guy for you, and you'll know it. There should be no question.
Unfortunately, the ONLY thing that can help you move on from a relationship is time. Lots of time. It sucks, but that's the only thing. In the meantime, keep yourself distracted with your girlfriends, and work on catering to yourself. Put all of your focus onto YOU and try to work on finding yourself. Don't reminisce for a while, save that for after you have adjusted to being single. You won't be as upset by it. This is the end of one part of your life, and it's the only way a new part of your life can begin.
I hope you can get through this, but know that you're not alone. You have other people in your life that care about you, and once you get through this you will not go into depression--you'll ultimately feel better after it all.