I'm not going to be understanding toward a person who lied
What did they lie about?
He told me he was going to give me a job opportunity first then didn't.
Well, if this was a lie and not a mistake then I think you're justified in being that way.  You don't need to spare understanding for liars!
I am glad you said so because I feel very strongly about this matter.
I think you are doing the right thing. It would be risky to give a second chance to a liar.