When you feel like someone is not being as thankful as you would like, or hoped. or maybe they don´t recognize how valuable you are. Or you feel like they are taking advantage of you, the normal response is feeling bad about it. Being sad, feeling cheated.
You have nothing to feel ashamed of. You were doing nothing wrong. You gave yourself with the best intentions. And if someone fails to live up to it, its on them. The shame should be on them.
And Karma will avenge you.