So in Jewish tradition, a man is obligated to have sex with his wife, and she with her husband. Their sexual needs and desires are each others' responsibility.

So if Mary and Joseph never have sex even after Jesus was born, that implies neither of them wanted it. Which makes Mary a VERY unusual presumptive-teenage girl, but she could be asexual, sure, immaculate conception and all. Joseph, on the other hand, has to be a functioning heterosexual to have fathered other children.