I know that sometimes it is better to keep something to yourself and not tell someone. But I think it is also not wrong that it can be worse when someone finds out what you're hiding from them by themselves.

You lie because you are afraid of someone's reaction when you tell the truth. But maybe you'd wanna do that only when you have good intention. To protect someone else, to protect them, or anything. Never lie when the only reason is just to protect yourself, just to make sure they keep liking you. It only means you're self-centered, you want them to see you the way you want to be seen, not the way you really are. If they are meant to stay, they'll stay. If they're not, they'll leave. If you lie for your image's sake, the relationship between you will then be the lie itself.

Never disappoint someone by lying or making excuses too much. It makes it hard for someone to trust you. Moreover, it tends to get really nasty at a certain point.