In Tennessee William's A Streetcar named Desire, how far can we say that Stanley is sincere to Stella?
we must take into consideration that when stanley looks at other women he thinks about perverse things....
Stanley is really exercising what he feels are his rights "as a man" to be a chauvinist and a misogynist. This is quite independent of his actual feelings for Stella which, apparently, seem to be strong enough to put him to tears each time she leaves the home during one of their yo yo dysfunctional fights.
Stanley loves Stella, but he loves her in his chauvinistic ways which are likely manners taught to him by the males of his family. He is sincere to the extreme admitting what he does, and never hides his true persona, bad or good, from Stella.
Her dependency to Stanley is precisely that morbid behavior of his: His so-called "manliness", his animal instinct, his bestial behavior (even if it includes staring at other "broads" like he would say), all that is part of the package that Stella completely bought and cherished.