No means no!

how do you tell a guy that you want to save your self intul your married. im really in a jam because he doesnt understand (1) he walks on me in the shower (2) hes always looking for a way to get a glimse on my body. and 3 I found a pair of my panties on his room. we are engaged by the way. I mean is this behavior normal in a guy? why does he do the things he does?

Are you living with this man? How does he have access to your underwear and you in the shower? Lock the bathroom door. How old is he? Perhaps he is just immature, but if he is not respecting your wishes now you should think about whether he will do so once you are married.

Think about what you are allowing him to do sexually, what you say to him, and how you act. Be careful about sending mixed messages. That said, a decision to wait until you are married should be agreed upon by the couple, and enforced by both of you, so one person isn't always responsible. There are other ways to be sexual without penetration, have you talked about that?