Byron is decrying the limited choices that women have in life in this stanza and indeed throughout the poem. A woman must put up with a man's "injustices" (drunkenness, unfaithfulness, etc) because their "sole bond" is marriage. A woman of any kind of means had few choices. It was not like they could go out and get a job and support themselves. For the majority of women, all they could really count on is that their husbands would betray them, in some or many ways.
So they learn to "conceal" their desires, even as they await the man who "buys" them in marriage. The woman may become "treacherous," thinking that another man, not her husband, will be a better bet. Sadly, the lover too will eventually seek another woman and betray her as well. At the end of her life, the woman will end up "nursing" her unfaithful and callous husband, until she or he dies. It's a vicious cycle that the protagonist, Don Juan, and his many lovers, does nothing to quell.
You can see how Don Juan's relationship with Haidee would fit into this cycle. While the two seem to share a greater connection than Don Juan had previously enjoyed, Haidee is still justifiably afraid of her father. So she "conceals" her desire for Don Juan. She is still, in most senses, her father's "property."
Haidee could lust after Don Juan, only to marry him, but, if history is any judge, eventually he will cheat on her too. If she sticks around until the end of his life, then she will likely care for him in his declining years til he, or she, passes away.