I'm going through something similar. I won't hijack your post by useless details. I just mean to say I understand what you're going through, I really do.

The way I like to reassure myself is in two ways: The first: don't cry that's it's over, but be happy that it happened. Remember that things could have taken a different course entirely. You could have never had the beautiful feelings you experienced together. You could have never tasted the love altogether. It could have never happened. But it did. Appreciate that it did. Appreciate that you were one of the lucky people who was able to live this experience for a whole ten months. The lessons you learned, the experiences you had, you will carry with you for the rest of your life.

The second: Let me use "addiction" as my analogy here before making my point. A person addicted to cigarettes, cocaine, heroin, alcohol etc whatever you call it, upon embarking on a journey to quit, could never envision himself without the comfort of his addiction. But if he makes it down the road and actually reaches the light at the end of the tunnel, he realizes that he was just under the influence of the addiction. The addiction was influencing his mind and clouding his reason. It was so remarkably powerful in making him truly believe that life without the addiction would be impossible. But it was lying, and it was a facade.

I like to compare attachment to a previous relationship to an addiction. In fact, I think I need not even "compare" because attachment to a previous relationship really IS an addiction. Whilst you're in the middle of it, the addiction really clouds your reason and feeds you poisonous thoughts along the lines of "you lost everything", "you'll never find someone like him/her again", "it will never be the same." But if you rewind back in your life, you'll remember that once upon a time, you also loved someone, and for some reasons, it didn't work out. But you forgot about that someone, and you moved on. And you loved another someone and it all started from scratch again. You're in that phase now. You're in that post-relationship depression stage and the "addiction" is poisoning your mind. But you have a very important weapon at your disposal now, and that is clarity. The clarity to realize that as hard as it may seem, and as attached as you may be right now...it is without doubt that you will find someone whom you will develop the same feelings for, if not more.

Stay strong.