Are you sure she wasn't seeing this other fella while she was seeing you?
Even if she wasn't, she's cheated on him with you.
If the roles were reversed, her girlfriends would be saying to her "He just wants his cake and eat it." Have a think on this idea?
I've been in your situation, and wasted 10 years of my life chasing the 'perfect woman' who, (in my case) had the morals of an alley cat. It won't be easy, but experience tells me you'll never be happy with her, no matter how much you believe you need her.
Love is blind true enough, but it don't have to be daft too.
Be careful who let yourself
want.