Praise be to Allah.
If you do not want to marry someone, there is no sin on you, even if he is righteous, because marriage is based on choosing a righteous spouse with whom you feel at ease, unless you dislike him because of his religious commitment, in which case you are sinning in the sense that you dislike a believer, because the believer should be liked for the sake of Allah, and in the sense that you dislike his adherence to his religion. But even if you like him as a fellow believer, you do not have to marry him so long as you do not feel comfortable with him.
And Allah knows best.
Al-Muntaqa min Fataawa ash-Shaykh Saalih al-Fawzaan (3/159)