we talked about it and decided a marriage between us probably wouldn't work for a lot of reasons, which sucked because we really click, but we click a lot better in the champaign/lawschool bubble than we would being married, having kids, etc.
had to make the grownup choices.
here is the deal about this- humans are horrible at predicting what will make them happy in the future. horrible. that's a fact.
i'm sure you both think you are making the right decision or whatever, but are you? also, marriage? jfc man. half the people that end up going through with it because they DO think it's right for them, end up divorced. how about you two little dipshits tone it back a notch and just enjoy each others company and see where it goes? 
I mean. we'd been enjoying each other's company for 18 months. we both want to get married someday and have a family. but when we talked about the logistics of it, we both decided we probably wouldn't work long term and we didn't want to keep on going knowing that this relationship we were in had an expiration date. i think a relationship like that would feel like fool's gold.
and rust, no it wasn't all about religion, although that certainly played a role. really, i don't want to get into the whole thing and wackycat it up here on gE (no offense wackster). anyways, the reasons are basically trivial at this point since it's done.
I think a large portion of people would be better off if they allowed themselves to be content with the idea of being single.
Also, they should stop being sentimental. It's such a useless emotion and I'm not sure why we have it.
being sentimental is my greatest vice. it's really a terrible habit.