Thomas Wyatt's sonnets express problems with love, and this one is no exception. The speaker first says there are three kinds of birds: those that see clearly by light of day, those that see well at night, and those who are attracted not to healthy light but to dangerous firelight. They want to "play" in it and find out it is not what they thought. In other words, they get burned.
The speaker likens himself to that third kind of fowl or bird, the one that likes to play with fire. The speaker can't not look at the beloved who is dangerous for him. His eyes are swollen with tears because of her—she has hurt him in some way—and yet, he ends the poem as follows:
My destiny to behold her doth me lead,
Yet do I know I run into the gleed.
A gleed is a fiery coal or ember. The speaker laments that although he is fated to be attracted to this woman, he knows she will hurt him just as touching a fiery coal would.
Wyatt expresses a common theme of love: we are often attracted to people we know are bad us, yet we can't seem to resist their allure. Head and heart are at odds. We know, logically, that the beloved one will hurt us, but our emotions take over.