Never figured I'd be driving over to a girl's house so she could dump me

"I actually tried, harder than many things that I've tried at before to make this work"
If you had to try it was not right and these are your own words.

I would not call what just happened a rejection? from the sounds of it you had reservations about the relationship also. Don't focus on the fact that she did to you before you did to her. She ruffled your pride a little and it is ok to be humbled every now and then.
They are all learning experiences good or bad take the lessons and move on. Her hard life is something she needs to grow from. It is not your responsibility to heal that for her, you cannot even if you wanted to. Codependency.

I have had many bad and terrible relationships some really are still my friends
I am with a girl now where we both have the same interests and we do not argue have not in the 5 years we have been together. Most importantly she IS my best friend.