To the op.
I'll put it simply, and I've been there.
There are two issues here that are making you crazy.
1. The hurt of losing someone you love. And not being loved back
2. A sense of injustice. That you have done so much for her, emotionally and materially. And she in the end treats you like garbage. This feeling of being disrespected/ taken advantage of makes you unable to see straight. You want at least to set the record straight, have her acknowledge the wrongs she has done to you. It's like getting ripped off at a store. You fume about it for days. Now multiply that by the years of your relationship, then by a factor of a few thousand because of the feelings you still have, and it puts you in a situation where you can't see straight.
Get over the injustice part first. It's not fair, it's not right, but as others have said she has done you a favour in the long run by showing her colours this way. Imagine you got married, a few years down the road you get cancer, in an accident whatever, and you need her, and at that time she decides she needs to be "all about herself".
I've been through a couple hard breakups in the past. One ended a bit like you. We had an intense, intimate relationship for a couple years. She had a lot of troubles through that time, and I was instrumental in helping her survive that. For a variety of reasons the relationship ended, and that hurt but what hurt more was she treated me like garbage. Wouldn't even show me the courtesy of sitting down with me and letting me go, talking to me. Instead she stopped communicating with me. And when I objected to this she called me selfish and inconsiderate. I got over that, but the sting of how she so easily disregarded all the times I'd been there for her still gets me.
A while later another relationship. A woman who I probably loved more than the first. Agsin, complicated reasons and she decides to end it. She sits down with me, explains where she is at, doesn't ignore me when I'm hurt by this. Tells me how much I meant to her and always will.
Now #2 was probably more likely someone who I could be with forever. Yet I was able to accept the breakup easier. That was a lesson to me that despite the fact that emotional loss and feeling unjustly treated are two things that get mixed up into one bad feeling, but are separate. Separate them in your mind. See the poor treatment of you as how she would inevitably treat you, when you needed her the most. As the others have said she has do e you a favour.
The emotional loss will lessen with time. To have cared about someone deeply does enrich you as a person and will better equip you for the next great girl.
Read your post and pretend you are a guy like us. You can't help but conclude you are better off.