Why am I thinking about these two failed relationships?

So, in October of 2018, my longtime girlfriend of 6 years ended things for good because of our religious beliefs.
Just because of the strain she had on our relationship, the breakup was actually pretty fine. But I was still heartbroken. I saw this girl in my suggestion on Facebook I knew in highschool, she accepted and we started talking. She unfortunately went to school 2 hours away, but would graduate in a year, and she had a month break coming up.
We really got to know each other and she opened up so much and we both said we'd want a relationship with each other if we had in person chemistry.
Well, we went out and it was awful. She was dead silent and cut the date short. She apologized several times and said she wasn't over her ex. After a few months, she pushed me further and further away and I just gave up.

In August, I asked out this absolutely beautiful girl. We went out twice and had a blast, them she disappeared. Months later we got in contact again, and we went out again. She explained she got caught up with family issues, got into drugs, and a few bad relationships but moved home and is sobering up. She said I was the only person to check on her and we had really, interesting?, Sex that night.
She got kinda weird and I told her I really liked her she pulled away and said she needs to find herself and get her life together.
I later found her on tinder and confronted her, she said she didn't know who I was while we texted. Once I said who I was, she said the account was old and she is trying to sober up and get better and doesn't want to hurt me. I deserve better and she's a lost cause. How I feel about her isn't real.

I don't know why, but I still think about both of these girls a lot. The first girl especially, because we had an amazing connection and it's a question of what could've been.
I more worry that the second girl is gonna wind up dead or something.
I'm not sure what to do...
Why am I thinking about these two failed relationships?
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