Strephon, your breach of faith and trust
Afford me no surprise;
A man who grateful was, or just,
Might make my wonder rise.
That heart to you so fondly tied,
With pleasure wore its chain,
But from your cold neglectful pride,
Found liberty again.
For this no wrath inflames my mind,
My thanks are due to thee;
Such thanks as gen'rous victors find,
Who set their captives free.
Laetitia Pilkington is not surprised by this man, Strephon's, betrayal. Rather, she expected it. Anyone honest would have just made her wondrous. When it comes to matters of love, feeling utterly vexed over one's feelings for someone one knows is bad for them is an old problem indeed. It was true in the early half of the 18th century when Pilkington wrote this, true today, and true thousands of years ago. She writes honestly and directly.
It's worth noting that "fondly" as it's used in the second stanza doesn't have the same meaning we think of it having today. "Fondly" then had the meaning of "foolishly" and as such, the stanza makes more sense. She stayed foolishly attached to Strephon because of the pleasure she took in being with him. Thanks to his cold negligence though, she found her emotional freedom once more, and thanks him for being such an ass that she was able to get over him.