Boyfriend wants me to wear a diaper because he thinks it would look cute is this abnormal I don't mind but should I do it?

That is up to you. How do you really feel about wearing them? If he wanted you to use it would that be okay with you? If he wants to change you is that okay with you? If he wanted to treat you like a baby would that be okay with you? if he wants to take you out in public while wearing one under your cloths is that okay with you? Can you trust him not to take pictures and give them to all his friends? if you can answer yes to all of these then it might be okay to do so. but I would find out more about his motives and if you are comfortable with them and if he will let to stop if you find that you can't stand wearing them. I also would try wearing one by myself with out anyone around to see how you really feel about it, you wont know till you try.