Help! Why did this all happen if we weren't going to be together?

I started seeing a coworker back in 2013. We went out a few times but we didn't date for a while because she was also casually seeing another co-worker too. She didn't talk to me after I decided to stop seeing her and she expressed her displeasure when I left the company not long after.
3 months later, she reached out to me on Facebook and she wanted to try dating again, and to be exclusive. We dated for 6 months, but we separated due to her religious beliefs. I was very upset.
Through 2014 and 2015, I had a hard time with the breakup because I started to fall in love with her in those 6 months.
After a really vivid dream in November of 2015, I reached out to her and we discussed our break up. She said I really hurt her, and she thought I would have called not long after the breakup, and said she didn't care about me and said she didn't want to have anything to do with each other.
Roughly 6 months later she reached out to me, saying that the holy ghost told her to. We talked about things, and she said she lied. She thought about me a lot. Through 14 & 15 she would look at my Facebook and ask my family how I was doing.
We wound up making up and starting to date again. She still Expressed concern of the religious stuff, so I went to church with her a few times, but I couldn't convert. She said she'd try to make it work. She had already committed to go on a mission, and I proposed to her before she left and she said she would accept when she came back.
She left in her mission, but pussed me away and argued with me saying she was doing nothing wrong.
She ended things, and I tried twice to fix it on her mission but nothing. She just tried to convert me. Then she stopped answering.
I ran into her after she returned and blamed the relationship not working on me. We had an intense conversation and she walked off.
But it still seemed she was looking at my Facebook, and she gave me a 'miss you' look last time I ran into her.
But I found out recently she is engaged...
Help! Why did this all happen if we weren't going to be together?
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