<human>: Give me the gist of the text in a nutshell

My girlfriend of six months and I been going through a bit of a rift lately, and it all culminated into a big conflict last night. 
I'm going to try to fill you guys in as much as possible without convoluting anything or ranting/getting emotional. 
We met at work last Summer, and it started as just a random hookup. But I was so attracted to her in so many ways and didn't want it to stay at that. I pursued. 
We had great times together leading up to us jumping into the relationship, and things have been the opposite of difficult throughout. 
This past month, though, things felt different. I poked and prodded at her pretty constantly, attempting to figure out what was wrong, to no avail. 
Last night I called her out on it (with probably not  the best empathy for her feelings) and she said she wasn't happy and it wasn't working out. I was quite shocked, to be honest. 
Eventually, I got it out of her: one of her friends from high school. She's known his for ten years, but he now lives across the country. 
She says that she doesn't want to commit to anything long-term with me (despite her strong feelings for me) because she can't stop thinking about scenarios of her future that include this other person and not me. 
She says she is still willing to take this one day at a time, with no guarantee she wants anything more than what we already have (and possibly even less). 
I don't know how I feel about this. I am so very committed to her and would love to feel that reciprocated. 
What do you guys think is the best course of action? I think it's worth my time to see where this can go, but I'm admittedly hurt and scared to invest anymore of myself in this. 
Help me put this together in my head.
<bot>: My girl confessed her lingering feelings for someone from her past and that she doesn't want to commit to me in case anything could possibly materialize between them.