This song has always puzzled me. Why was she so upset that he would be careful - did it show a lack of passion? Is it one of those ça se fait sans s'demander things? Or is it just that she wouldn't lie down with anyone and used that as an excuse? I never got it. What do you all think?
My father, on the other hand, could see how he could mount her on a horse, he just couldn't picture how he could manage to mount himself upon another. My mom had more trouble with the description of their pair as sibling-like. Anyway, here are the lyrics:

(Can't recall title, it's on Faithful Lovers and Other Phenomena, by Cynthia Gooding)

There was a knight and he was young a-riding along the way, Sir
And there he met a lady fair, among the cocks of hay, Sir (bis)
Quoth he, Shall you and I, Lady, all on the grass lie down-O
And I will especial care of the rumpling of your gown-O (bis)
-If you will go along with me unto my father's hall, Sir
You shall enjoy my maidenhead, and my estate and all, Sir (bis)
So he mounted her on a milk-white steed, himself upon another
And thus they rid upon the road, like sister and like brother (bis)
But when they came to her father's hall, which was moated round about, Sir
She stepped straight within the gate, and shut that young knight out, Sir (bis)
Here is a purse of gold, she said, Take it for your pains, Sir
And I will send my father's man to go home with you again, Sir (bis)
And if you meat a lady fair as you go through the next town, Sir
You must not fear the dewy grass, nor the rumpling of her gown, Sir (bis)
And if you meet a lady fair as you go by the hill, Sir
If you do not when you may, you shall not when you will, Sir (bis)

Actually, it was the very last line that took me some effort to untangle as a small child...