What I recall hearing as a young Catholics, was that Mary was always a virgin because she was sinless.
And I have had Catholics tell me that in the past.
IOW, sex is a sin, and Mary would have been a sinner had she had sex as any wife would with her husband.
The Bible reports that in accord with the requirement of the Mosaic Law, 40 days after Jesus’ birth Mary offered at the temple in Jerusalem a sin offering for purification from uncleanness.
She, too, had inherited sin and imperfection from Adam
Lev. 12:1-8