Nothing Feels Right Anymore...

She felt like you hated her but still loves you? Did you do something to make her think this? There's a lot missing to this story. She seems to love you, you love her, where did the miscommunication come from.

Break-ups are always hard, especially if you loved her. If there is no chance of getting back together, all you can do now is wait for the pain to lessen.

Dating other people isn't going to help, because you're still thinking about her. Give it a little more time. The lack of motivation might be with you for a while too, but you have to force yourself to do things. If you stay in bed all day dwelling on it, things will only get worse. So live your life normally. Do what you usually do, and try new things, if you want. Try having fun, or doing something that will make you feel good about yourself. Don't avoid or ignore your feelings, but don't let them bury you.

I know how difficult it is, and I wish I had better advice. Be patient, it will get easier.

How long has it been since you two broke up? Why do you feel like you let her down?

As Locke said, it does take time to get over a breakup and lying in bed without motivation to do anything will only cause your depression to linger longer.
Meeting people and going out is okay, but I don't think I would date until you come to terms with what happened.
I've been there as well. All you can do is try to stay busy, try to keep your mind off of it (and her) until you are able to function without forcing yourself.

I know it is hard to understand this right now but people just drift apart, it is part of life, nothing lasts forever. So, you could try turning to your other friends and devote more time to them, eventually you may get a new best friend, who knows

I'm on the fence about that. Marriages can last forever, I've seen it first hand...lots of them actually in my area. But are they perfect? Nope, not in the least. I can't tell you the number of love/hate relationships I know of. And they've lasted "forever"

I'd say your feelings are pretty normal for your situation. Time IS a great healer