Love is a very powerful emotion that can bring great joy and fulfillment to people's lives. It can also, however, bring considerable grief, suffering, and emotional pain. It can drive people crazy and make them do all kinds of things that they ought not to do and otherwise wouldn't do.
The downside of love forms a running theme throughout the poetry of Sir Thomas Wyatt. As someone whose passionate love for Anne Boleyn, second wife of King Henry VIII, was never requited, this shouldn't come as much of a surprise.
In the supremely ungallant and ungracious "Ye Olde Mule," Wyatt paints a decidedly unflattering portrait of his would-be lover. He accuses her of powdering her grey hairs to make herself look more beautiful. It is likely, if not absolutely certain, that Wyatt is referring to Anne Boleyn here. But even if he isn't, there's no doubt that the poem is motivated by anger and churlishness at being rebuffed.
In "They Flee From Me," the speaker is a man who once loved many women yet now loves no one. This is because the speaker seems to have been hurt by an unfaithful woman who shamelessly took advantage of his good nature.
Elsewhere in his work, Wyatt writes of the joy that love can bring. But it is more common to see him deal with the emotional pain, the suffering, and the utter disillusionment that love in all its terrible power so often leaves in its wake.