Collocations for resentful - adj.

be, feel, look, seem, sound
become, grow, remain
They grew bitter and resentful.

extremely, fairly, very, etc.
bitterly, deeply
They were bitterly resentful of the fact that they had to work such long hours.

increasingly
a little, slightly, etc.

about, at
She felt resentful at the way she had been treated.

of
He was very resentful of their success.

towards/toward
He felt deeply resentful towards/toward his ex-wife.