Love is complicated. You don't really know what it is or what it means until you achieve it. Being infatuated feels like love but it lacks the work that love takes. I have no doubt that she felt something for you, but it may have not been love. She met someone, spent a lot of time, experiences got married. Her definition of love may have changed, while yours did not. Spending years apart doesn't strengthen a relationship or connection. It sucks and it hurts a lot but you have to move one and accept that it's not meant to be. It's not easy and you can't just do it, but baby steps.

It's hard to get into a new relationship when you are entrenched with someone else. She has a husband, a life of her own and torturing yourself with what things could or should have been won't change that. It only makes you suffer.

She isn't the only person in the world and there is someone out there that you can make a connection with. As much as the rejection hurts you just have to keep trying until you find a relationship that works. Don't think perfect, think real. Find someone with common interest, that both have a mutual attraction. If you asked hundreds of women why did they say no? If you have never asked maybe you can probe a little further if they say no and ask if it is about looks, or your approach or some distinct reason that put them off. Do you come off as not being confident or shy? That is a major turnoff for a lot of women.

Since this is impacting your life so much have you thought about seeing a therapist? Therapist work on things beyond mental illness. There are family/marriage therapists and similar out there that work on relationships. Even if your not in a relationship you could talk to someone and take a deeper object look and find an approach to get in a better place.