How do I heal and move on from this?

I was dating who I believe was the love of my life and we had come off a few years of being separated. She was a part of the Mormon church and because of that my parents didn't like her, and her parents despised me.
I literally poured everything I had into the relationship. We had to mend things from our break up, I fought weekly with both of our parents to try to make things right. I would help her family with things and I even drove out to rescue her mom after she broke down because I was a mechanic. I even went and had a heart to heart with her mom to try to make peace and it made major progress.
My girlfriend did decide to do a mission, and her family was on me for not being supportive, because it was hard knowing she was going to be gone for almost two years. I still bought her new suitcases and bags for her mission because her family struggled to pay for her mission.
I had asked her to marry me before she left and she said she'd accept officially when she came home. I even tried going to her church several times because I knew how important the church wedding was to her. But I couldn't devote myself to that religion.
But she changed her mind on the mission and decided we couldn't be married and kicked me out of her life. Despite writing the most heartfelt and open letters to her, she only wanted to convert me.
I thought that once she came home she'd come off the mission high and we'd get back together. But she instead cast the faliure of the relationship on my shortcomings and faliure to convert. She made me feel she didn't truly love me and perhaps even faked it.
I ran into a few Mormons and they told me they thought with time she'd come to her senses and come back because I was her rock. They even went so far as to say she'd disgrace the religion if she went back on her promises and devotion to me.
Much to my absolute devastation, she moved on and is engaged to someone else. What can I do? I gave everything I had to make it work with her.
How do I heal and move on from this?
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