First off 2004, sorry to hear it man. That is never an easy thing. And no matter how much people reply to your question, you won't find any answers to the pain. Sure you will get thoughts from others that will guide you back to a "happy place", but it is all on you to figure out how you need to get there.
I will share with you my saga. (the short version)
Got married 8 months after meeting the girl of my dreams to the tune of a $15K wedding. Less than a year later skeletons come out of the closet, she is bulemic & a raging (hidden quite well) alcoholic. Not to metion her ability to lie about EVERYTHING. So I try and get her help, does not want to change. Figured out I had almost $10k unaccounted for which god knows where that went. I cut my losses and call off the marriage before we end up with a child. Also find out she was in constant communication with an ex.
Her daddy is a divorce attorney.
I am wiped out at that point, 3 cars and an entire househould of furnishings goes buh-bye.
So there I was 6 months ago, 3600 miles from my nearest family member, no car, no furnishings, no real cash to speak of. And completely broken hearted at the thought of what we had initially planned to be a lifetime.
Present day: Put together enough scratch to buy a 92 XJ, put some elbow grease into and turned it over, picked up a 97 TJ 2 months ago and have dumped every weekend into it. Taken all the negative stuff I had built up and worked it instead.
Now I find myself on Friday nights at 6pm loading up the rig, grabbing the dog & my tent, and just driving to some kick butt location. All by myself.
IT IS SO THERAPUTIC
My opinion, get out before she has a chance to hurt you more. If she still loves him and has point blank told you that, she can not be trusted. She has obviously been telling you that she loves you as well, and as tough as true love is to manage, there is no way to split it up between two. So she is lying about her love to one of you. There is one of you that is supplying her with a comfort zone, a place to live, the comfort of having somebody there every night. Meanwhile her heart is somewhere else.
I am hoping and assuming there are no kids, because obviously that would be more difficult to just walk away from.
But if there are no kids, walk away. Be civil, split up property as best you can, take a loss if you have to. But just get yourself out of the situation so you can sit on a boulder somewhere overlooking a river to hash things out.
And don't beat yourself up over it. She has made her decision, she made it when she told you about the ex. Now make yours. (just make sure you keep the jeep!)(it will help with picking up chicks when you are finally over her!)
Good luck man