GRUDGE
Resentment, a feeling of resentment or ill will, especially one lasting for a long time. (noun), Accept or admit unwillingly (verb)
If you have or bear a grudge against someone, you have unfriendly feelings towards them because of something they did in the past.
BOTTLE UP
To contain, hold, or entrap something or somebody, especially a group of people or to conceal or repress strong feelings
Examples:
1.She just burst into tears because of all the resentment she's been BOTTLING UP for years.
2.The young woman BOTTLED UP her feelings for an older man.
3.The manager of the company BOTTLED UP all the employees for a quick meeting.
4.I used to BOTTLE UP my anger when I was a kid.
5.It's not good to BOTTLE UP your feelings for the person you love.