You feel like crap, because you have broken up with your girlfriend. Regardless of the circumstances you would have, it is perfectly understandable. If she was not going to be able to stay with you long term without resenting you, it would only have become worse as time went on.
It sucks, but it will pass eventually.
My ex and I were married for 25 years , but I wouldn't have felt any different if it had been a month.
Karen.