When the change in his feelings took place there is no means of knowing.

He does not seem to have been a passionate man, nor a very ardent lover, but there is no doubt that at this period he inspired the girl with a very real devotion and respect, even though perhaps her heart was not deeply engaged.
Montagu would have had the girl find her pleasures exclusively in books and in his own conversation.

She, at the age of twenty, on the other hand, was full of the joy of life and liked the various social pleasures that came her way.

Naturally, she tried the effect of her good looks and wit on men.

In fact, she was fond of flirting, and as it must probably have been impossible to flirt with Montagu, she indulged herself in that agreeable pastime with more than one other--to the great annoyance of that pompous prig of an admirer of hers.