Geoffrey was far from being Matilda's own choice. Women generally didn't get choices in those days. Aged 12, Matilda was married to a man of 28. Then as a 26-year-old widow she was married to a boy of 15. They did not get on, but no one but her and presumably her husband cared so long as they had children. Both marriages were made in pursuit of her father's policies, and he was not a man for even near kin to flout. Had Matilda gone off and married someone, and it wouldn't matter who, without his consent she would have been better never to come within his sight again. For sure he wouldn't have worked in the way he (unsuccessfully) did to ensure her succession, but would probably have anointed Stephen or some other nephew himself.