How compromising/accepting should you be in a relationship?

How far and with what kind of aspects do you fluxuate with? I was raised told that no one is perfect, and that all relationships need work to survive. So is there "the one"? I will, and have, gone out with anybody I'm attracted to. The rest I deal with through patience and understanding. One thing I'm let down on is that my current gf doesn't really stimulate me intellectually. Where is the line when coping with this? It can't be changed basically bc it is her personality; but on which things do you decide to work with and to not work with? I love her to death, but in this aspect it is killing me bc we are talking (she) marriage. I feel too bad hurting anyone. I love her so much. She is so sweet and good-hearted.