Lear and Gloucester are both very similar in that they are betrayed and stripped of power by their children. Both wander as outcasts after having been powerful and high status people.
A chief difference is that Lear willingly gives away most of his power to his two eldest daughters based on their empty words. He has been in charge and deferred to for so long that it never occurs to him that this situation could end—it seems as natural as the sun rising in the dawn. As his Fool points out to Lear after he divides his kingdom, he is a bigger fool than the Fool himself. With his eyes open (if not seeing), Lear create the situation that puts him in his daughters' power.
Gloucester, in contrast, is manipulated by Edmund without any realization of what is going on until it is too late. He does not put willingly power into this illegitimate son's hands and hope for the best: he is deceived by his son in underhanded ways. He is trusting, but he trusts what appears to be the evidence of his senses: Edgar, to any rational person, might seem to be a traitor because of the way Edmund manipulates events. Here, Edmund creates the situation that strips Gloucester of power.
While both men are the victims of ungrateful and evil children, they react differently. Lear, who does not like to give up his illusions, retreats into madness to avoid fully dealing with his new reality. Gloucester, though blinded, gains insight. He faces reality, and therefore, wishes to commit suicide, though Edgar prevents it.