I'm going to lie to someone that I wasn't home
What is the point in lying to someone about being home?
I'm going to steal something from the house and I don't want her to know.
It is wrong to tell lies. It is also wrong to steal. Others will lose trust in you.
It doesn't really matter if she doesn't trust me anymore because I'm planning on breaking up with her anyway.
Just be careful because the more you lie the more difficult it will become for others to trust you. It may get to the point where people are not believing anything that is coming out of your mouth.