prentending to be happy even though youre not
is extremely draining, and the more you do it the more you will get sucked into a self destructive spiral.
Unfortunately I think about 99% of any job that interacts with customers or the public demand it.
Unfortunately, parents tend to suck and crappily teach their kids it's better to sacrifice for the benefit of another, to help with their burden while trying to avoid being one to others.
"Stop crying, you have to share, don't act up or you don't get to go, be nice, be good, be respectful of others."
Unfortunately, most of life teaches you to be a punching bag too.
"Don't fight just walk away, if someone hits you your life is full of police and paperwork unless you just take it, if you hit someone your life is full of police and paperwork and jail and you don't get a choice, no one cares about your problems everyone has their own problems, be a friend and maybe someone will be yours, hope for the best prepare for the worst."
The only hope you have is when you become an adult you can go out and build your own family. You can find friends and date and find specific people where when you're around them you never have to pretend to be happy when you're not, you can simply feel how you naturally feel, you can speak your mind, and you can make that family where you spend most of your time and energy with.
That's your choice. Lots of hard work, though.
But the rest of the time?
Civilization. Civilization = suck it up to get along. There will be reciprocation. It's in the social contract. The more you push your problems on others, the more they'll push theirs on you. And there is a lot more of "them" than there are of "you." So suck it up, pretend happiness, escape to the family you build. The only place you can truly be yourself.