@eatyourveg No, Valentine (Elizabeth's son) never dates Clowance, though Ross and Demelza are always worried about the possibility.
In regards to his paternity, it's never publically revealed, they obviously didn't have paternity tests, but Ross and Demelza both know he is Ross's son, and Ross basically admits this to himself near the end. Other characters, including Verity, seem to guess as Valentine looks very much like Ross and Ross's father, but there is no public accusation or reveal if that's what you mean.
However, Valentine guesses the truth and even asks Ross at one point. I think all the characters knew the truth, but they all keep quiet about it.
@FaithEverPresent The scene is even more rapey in the books actually. Here's how it goes:
Elizabeth: “Ross, you can't intend. Stop! Stop, I tell you.”
But he took no further notice. He lifted her in his arms and carried her to the bed.
Later on Ross remembers the scene and says she stopped protesting and became into it (not those exact words!) so I think it's up to interpretation.