I need to see my ring before agreeing to marry my boyfriend.
Why do you need to see the ring first?
I've been cheated on two times before and I'm not taking chances this time.
While basing your decision on the ring is materialistic, it is okay to want to know how much somebody cares about you before making the decision. It will make sure things are clear and understood.
If he doesn't show me that ring then I'm going to leave him.
That seems a bit extreme, but it's certainly understandable that you want to make sure that your boyfriend really cares about you. I'm sure if you let him know why you feel the need to see the ring, then he'll do what he can to make you happy.