He's 'resentful' of his boss. = He feels 'resentful' toward his boss.
She is 'resentful' about being demoted.
a 'resentful' letter to the editor
(..) It was difficult. I didn't know if it work out, or we just both... I just thought maybe if you didn't make it the way you wanna make it, you would be resentful and we be unhappy. Who knows? I don't know. You know, I never stopped thinking about you. Not...not for one day. I still dream about you. (..)2016 Café Society