<human>: Can you give me the gist of the text in a nutshell?

I've been with my girlfriend since I was 18 and I'm proud to say we've been great and had a very strong relationship. We have lived together for a year and again on the whole everything has gone smoothly.
However, recently I came to the conclusion that I didn't feel the same for her anymore and thought we should break up. We talked for hours and we agreed to see how things go for a few weeks and try work on our issues. 
However, I've realised since that I feel this way because I've developed a crush with someone at work that I work really closely with (and I can't avoid). She is fantastic and while I know it's wrong, in some ways I want to pursue it. I know a lot about my crush, good and bad, and I still like her a lot. My girlfriend doesn't know I feel this way about this woman at work and Id find it incredibly difficult to be brutally honest.
Part of me thinks it's a crush and the feelings will pass and part of me feels I'm not committing 100% to my gf and that is wrong so I should finish it. 
I feel very strongly for my gf but I've had no other relationships of note so I cannot compare my feelings for her to another relationship. I feel it's make or break time for us. 
What should I do and has anyone had a similar situation?
<bot>: in long term relationship, not sure I feel same way, developed big crush, make it break for me and gf, what should I do?