I need some psychological/love advice. Can someone help?

No, there is absolutely nothing wrong with you. The reason why you can't get her out of your head is because you miss her. You want to be with her. You need her, and when she's gone you just feel so alone and lost, that's only because you love her, a lot. It's hard to move on and stuff, I can relate. You guys been together for so long now and it's not easy to move on and let her go. Especially when she was someone whom you loved very much and cherished. But none of it is your fault, people change and that includes feelings. Sooner or later you'll find someone else and get over her. It may not be now or anytime soon but maybe a couple of months or maybe years. This kind of feeling is not something that can be healed over a short period of time. For some people it can take them years just to forget that one special person. But just know that it's not a medical problem so you don't need to worry. I just hope things work out :). I hope this helped, if not then i'm really sorry.