Sexuality is a normal part of being human; the sex drive varies person to person though. I think sex is important in a relationship only inasmuch as other compatibility issues are important; if one does not get along sexually, there will be stress in the relationship just as surely as if one doesn't agree on finances or emotional expression or how to raise the children, etc.

Sexuality is part of one's expression of who a person is; for example, Pandoren's asexuality would not go well with someone with a high sex interest, as has been said. But sexuality isn't something that can be willfully controlled, anymore than breathing or eating can be; boys/men ejaculate in their sleep and I've lost count of the number of sex dreams I've had :-) It's a physical part of us.