They’ll come out sooner or later, so it’s better they be on your terms.
Life is inherently frustrating. You stub your toe, you can’t afford that nice thing you wanted, your job isn’t fulfilling, or any other number of little grievances have a way of piling up on you. This is also why people like complaining about things. Complaining is cathartic, it gives you a chance to put your feelings into something audible, and it’s pretty important to your mental well-being.
I have a little arrangement with my parents where if I’m scared, worried, or irritated about something in my life, even if it’s something silly and inconsequential, I can call them up and they can calm me down. As I’ve explained to them, sometimes I just need to be “audibly concerned” about something. This is why it’s so important to have a support network, whether it be made up of family, close friends, or trained professionals. There are some problems that you just can’t work through on your own; keeping frustrations and worried bottled up inside the echo chamber of your head won’t help you resolve them. You’ll just go around in circles until it’s all you can think about.
Think of your head like an old basement with a permanent leak. You need to periodically drain the water out properly, or else it’ll start bubbling up through the floorboards of your daily life. When you try to repress fears and grievances, they leak out at inopportune times, like when you’re trying to have fun or get work done. I speak from experience when I say that it simply isn’t possible to keep things bottled up forever. They will always come back up, so make sure you drain them out in a safe and constructive manner before your metaphorical carpet gets stained.