I don’t think they were ever married. She was one of the first ones I remember when I was in high school that was against marriage even when she had Ryan’s son. I assumed she agreed to marry him at the end for legal purposes? However, I don’t think they did.
You’re right, Farrah and Ryan never married (unless they did so recently and we don’t know about it). She was married to Lee Majors from 1973-1982 but never married Ryan. according to wiki