For heaven’s sake, don’t. The only thing this will accomplish is to cause you more pain.
That door is shut, and it’s not going to open again. Sitting in front of it wishing only keeps you from trying other doors.
I’m a little disturbed that you still seem to think she is the only person you could possibly “make love” with, the only person who could possibly be a good partner, the only person you could possibly have a happy relationship. Those ideas aren’t just wrong, they’re dangerous.
Go and focus on being a healthy person. Have adventures. Learn new things. Find a job you’re passionate about. Do charity work. Advocate for a cause. Be whole and well rounded, and leave her out of it.
Then consider the following: there are 3.5 billion women out there, and if you are an atheist, then it follows that the concept of “soulmates” or “true love” is just as ridiculous as Young Earth Creationism. We are random beings driving by genetic, social, and cultural imperatives. We are all capable of the kind of connection you felt when you were with this woman. That connection was not a measure of how perfect the two of you were for each other. It was confirmation that both of you had the human capacity for love and intimacy. If you believe that can only happen for you with her, you are doing yourself a terrible disservice.