wed,
That lord whose hand must take my plight shall carry
Half my love with him, half my care and duty.
Sure I shall never marry like my sisters,
To love my father all.

Cordelia is pointing out that her sisters' words are empty flattery. Surely, she says, they can't really love Lear as totally as they claim to if they also love their husbands? She says she, in contrast, will give her husband half her love when she is married and that Lear will get the other half.

Cordelia is trying to be honest to counter her sisters' deceitfulness and to suggest to her father that love is more than words and empty promises. Her speech, however, throws her father into a rage. He feels especially hurt and betrayed by her because she has been, as he notes, his favorite daughter. The last thing he expected was for her to insult him and seem to express disdain for his generous offer of the best of his kingdom. It feels to him as if she has rejected his love.

Goneril, once she has what she wants—which is her share of her father's land, wealth, and power—has little use for him as a human being. He very quickly becomes a nuisance who can offer her nothing.

Goneril expresses her frustration in act 1, scene 3 when she asks Oswald if Lear hit her "gentleman" for insulting his Fool. Oswald says yes, and Goneril expresses her exasperation with him, saying,

By day and night, he wrongs me! Every hour
He flashes into one gross crime or other
That sets us all at odds. I'll not endure it.
His knights grow riotous, and himself upbraids us
On every trifle.

Goneril is angry because Lear insists on continuing to act as if he is king after he has given up his power. She says he keeps interfering and trying to run every little thing. She was just a very short time ago completely flattering and loving toward her father, but now she speaks of him with contempt as if he is going senile, stating,

Idle old man,
That still would manage those authorities
That he hath given away! Now, by my life,
Old fools are babes again, and must be us'd
With checks as flatteries.

She is frustrated that he won't step aside and accept the reality that he no longer has power. She says he is going into a second childhood and is a "fool" and acting like a baby. She warns Oswald that the new "flatteries" Lear will be offered are "checks": in other words, he will be firmly told he can't continue in the way he has been acting, just as one would tell a child they have to behave differently. Goneril knows she has the power to control her father and is irate that he can't seem to understand that the dynamic has changed.

To some extent, she is right: Lear wants to have his cake and to eat it, too. He doesn't wish to bear the burdens and responsibilities of ruling any longer, but he still wants to be listened to and deferred to as if he is still a powerful king. Goneril is expressing to Oswald that Lear can't have it both ways and that she plans to make sure he understands his new role.

Goneril is angry because her father seems to like her younger sister Cordelia more than her or her sister, Regan. She says, "He always loved our sister most; and with what poor judgment he hath now cast her off appears too grossly" (I.i.290-92). Obviously, Lear has shown a preference for Cordelia all their lives and, understandably, Goneril resents this. At first, her anger can be understood as a reaction to poor parenting. However, by the end of the play, Goneril treats her father so cruelly that the audience is forced to sympathize with Lear. She even begins treating her husband poorly and calls him a "Milk-liver'd man!" (IV.ii.50). Thus, she allows what was probably a reasonable dislike over her treatment as a child to turn her into a miserable shrew.