This is my opinion:
no Godly man should make you take your purity ring off in exchange for his engagement ring. He should encourage you to put it before his ring, because well, thats where God & your commitment belongs, before or in front of him. If anything he should put it on your finger purposefully behind that ring. It should encourage him to know that you are dedicated to purity in other forms even through marriage & that God is still number one.
But, thats just my opinion.