It's unlikely that she deactivated her Facebook profile. She blocked you. It makes her invisible to you even if you type her name into the search bar. I know because my ex did this to me.
Though my relationship was much shorter than yours it was very intense and I invested heavily in my ex. She broke my heart, too. Just know that you're not alone.
Here's what you need to do to RECOVER AND MOVE ON. I'm not going to advise you on how to get her back because that will only lead to more problems and even deeper heartbreak. Been there, done that. It's not worth it. It's never worth it.
Here's what I've learned through lots of research, books, and even a couple of therapy sessions:
Step 1: Before you do anything else, you need to accept the fact that it's over. Take it from me, the guy who didn't do that even though he knew he should have: it's for the best, and pursuing her now is only going to make things worse. I made my ex hate me because I wouldn't stop pursuing her.
45 days is long enough to say that there were problems that you guys weren't about to overcome. Even if you managed to talk her back into seeing you again, it won't last. It'll go on for another two weeks, maybe a couple of months, but those problems will come back, and she'll end up leaving you again.
Look, I know that in the movies we often see that people break up, and then the man does something great to prove that he loves her and wins her back forever. That's Hollywood.
Here's real life: She knows that you love her, she knows that you care about her, and she's choosing to leave you anyway. It's not because she wants to hurt you. It's because the pain of losing you (yes, she's feeling pain, too, or at least did at first) was less than the pain of being with you. She didn't do this to hurt you; she did it because she honestly believes that she will be happier without you. I know it's hard right now, but try to remember to eventually forgive her and understand that she's just pursuing her own happiness.
As far as her moving on, keep this in mind: she had a head start on you. She was already thinking about leaving before she actually did. She was talking to friends about it, she was going through it in her head, and she was weighing her options, so she had already progressed through some of the pain when she finally cut the cord.
Step 2: No Contact Rule. DO NOT CONTACT HER ANYMORE! It sounds like she already cut you off, but she knows you're still trying and all you're doing is forfeiting your dignity and ultimately making her have even less respect for you. Again, I did all of this and I can tell you that it's not worth it.
Another thing: DO NOT fall into the trap of being friends. A man cannot be friends with his ex in the immediate aftermath of a breakup. It makes things too awkward, and it places an undue burden on you, the dumped, to pretend like you're not hurt. Don't do this. Cut it off. You can't be friends with her, not right now and not for a good while, if ever.
As far as how long, I would say "until you're ready to talk to her as just a friend," but if I do then you'll convince yourself that you're ready when you're really not and contact her because you're subconsciously trying to win her back, so I would say a MINIMUM of 30 days, but 90 would probably be better.
Step 3: As you advance through the stages of grief, denial (you're definitely still here), anger, bargaining, depression, and finally acceptance, make sure that you're focusing on yourself. Take on at least one new hobby and one new side project. Learn a new language, play a sport, write, do whatever, but make sure that you're improving yourself. This will boost yourself esteem and help affirm that you will get past her and move on with your life.
However, be sure that you let yourself feel your pain, too. Part of the reason men struggle is because our society tells us that as men we're supposed to "man up and tough it out." Of course you should do this eventually, but for now realize that she broke your heart and you have the right to be sad. Talk to your friends and family, write out your feelings, and cry. I'm serious, cry. By doing this you're purging these feelings instead of repressing them like most men do. Take an hour per day to let yourself feel sad. As time passes you'll see that you won't be able to cry for that long. It'll lessen each day, as will your pain.
Step 4: DO NOT put your ex on a pedestal. This is a mistake most if not all men make (I did it too). She was not perfect, I don't care what you say. I'm not saying she didn't have good qualities; if she didn't you wouldn't have fallen for her. However, she's just another person. She has her own imperfections and insecurities, just like everyone else.
Knock her off that perch and put yourself up there instead. Keep reaffirming that you're a good guy and that any girl would be lucky to have you. The fact that it didn't work out with this one person is by no means an indicator that it won't work out with someone else. It will.
Step 5: Take a lesson from this. At first you're going to be tempted to constantly try to figure out what went wrong. As long as you're going to do this (and you will, no matter what I or anyone else on here says), try to look at it with an objective mind and understand that you both contributed problems. No one is more at fault than the other; it just didn't work out. Still, take a look at some of your own contributing factors and make it a point to avoid doing those things in a future relationship. My personal flaw was that I was too clingy and self-deprecating, and it drove her away.
Above all, have patience. This takes time, it's not easy, and it's going to hurt. What I'm trying to do here is lessen the pain and help you get through it quicker. However, there is no way to avoid feeling some pain. You can, however, take and active role in it and help yourself get through it a lot quicker. They say that time heals all wounds, and while that is true, it can happen a lot quicker if you take an active role in it.
Here is a link to a free guide that helped me a lot. Go through it with patience and let it take a few days to complete. Do the exercises like guy instructs you, and you'll be well on your way. Best of luck to you.
Sorry forgot the link! Here it is:
The Breakup Guide