You've lost someone close to you and it's normal that you are hurting. It's normal if you can't believe it yet; you don't want to believe it. When people lose ones they care about, they can react in different ways - it's their own personal way of dealing with the pain they're suffering right now. Everything that you're feeling is normal.
I know what it's like to suffer the way you're suffering right now;.going through the stages of disbelief, blaming yourself, thinking you're never going to recover. I know how much that pain hurts. One thing that you have to accept is that the person you care about has gone. No matter how much you pretend that what has happened hasn't, it's not going to change anything. All that you're doing by telling yourself it's not real, is prolonging the pain.
I think that during grieving everyone goes through all the "What ifs?". Those "What ifs?" are not going to help you in the long run. YOU are not to blame for what is happened. Death will happen to everyone at some point in time, nothing can prevent that outcome in the long-run. Yes, now-a-days death can be delayed over and over but at one point, it will still take place. Whether you are religious, whatever your views on the afterlife, the bottom line will still remain the same and you personally are not responsible for this.
Are you telling yourself "I'm never going to recover from this"? I know that right now it might seem that way and I've been there. Right now you can't see a life without this person in your life, you may even think you don't want a life without this person. What I can tell you is it will get easier, given time. There will come a day when this person is not all that you think about, when your thoughts are not focused entirely on them every minute of the day. I'm not saying that you'll forget them, of course not. That person was a major part of your life and will always leave an imprint on you. Forgetting them is not the way forward either. What I'm trying to say, is that you will overcome this. There will come a day when you can think about the person who was close to you without remembering them for their death. You will be able to think and smile about all the good times you shared, all the precious time that you spent together, and more. I know that right now that day seems so distant, or even impossible. I know. I've felt the way you feel right now, but it will come. Stay strong; think about what this person would have wanted you to do. They would want you to be able to move on past this and to be able to get on with your life.
There will be people around you going through the same thing that you are going through. Let them help and support you and support them back. They understand how you feel, they have lost someone too. They're probably the greatest element you have right now.
The other people in your life don't expect you to be "fine" either . Do not be afraid to reach out and ask for help if you feel you need it. I'm sure that those who care about you hate to see you hurting and want to help you through this. Let them.