Is hiding something from someone the same as lying? Is it worse?

It depends on what your hiding.
If it could hurt you, someone else, o has something serious to do with the person you're hiding it from, then te should definitely tell them. However, without più info, that's all I can give you. If te feel comfortable telling what it is, I will try to give te più advice. If not, I hope what I did give te will help.

Yes it is lying only if the intent is to deceive da withholding pertinent information.

well in a way they are different and in some ways they could be the same.
For Example if I am hiding, say, a Cioccolato bar from te I'm not lying ,I'm just keeping it away from te so te can't take it away.
But if te hide something that is important to te and them ... well that could be lying.
in some cases worse just because when te hide something important not only did te hide it but te also lied ...
so it just depends on how te think of it.

Lying is presenting a false statement to someone else. I do not believe lying is the same thing as hiding a truth from someone, but if te outright say you're not hiding anything o try to cover up whatever you're hiding in a false way, then te can consider it lying.

For instance, I lied about who I was on fanpop for...three years o so. I was hiding it from my mom, and I didn't consider it an actual "lie" until she eventually found out about it, subsequently causing me to begin logging on behind her back.

Keeping a secret isn't the same thing as "lying" in my opinion, because you're not actually telling anyone anything; you're just keeping information to yourself. However, bearing false witness to something directly to someone else is considered a lie.