It is all chemical
I know I said I was not going to give advice buy I am worried about you so I have to say something.
It is all chemical buddy. There are neurotransmitters in your brain that trigger pleasure. You circuitry has become highly dependent on her as a stimulus and you are going through a major withdrawal. Getting over this might be as hard for you as say a heroin addict cleaning up but with time your body will re equilibrate. Yes, you may always long for her and some days will be better than others will but you will not always feel the way you feel now and you will be perfectly able to have wonderful days.
There is something else to consider. You were able to have the relationship you had because of who you have been in the last 3 years. You may not have been capable of having such a powerful connection 20 years ago. You may very well make another strong connection; you can’t rule that out. You can not apply your statistics to this and simply say, “I met one person I could have this kind of connection with in 50 years, what are my odds of it happening again” because you are not a constant. You are a variable and you have no idea if life still has plenty of wonderful surprises for you. My guess is that life does indeed.
I hope that at least the thought counts if the content of this email is of no use to you.
Get well soon : )