Am I a bitch?

Don't get me wrong I love my fiancè and everything about him, we got engaged a year ago... I'm happy with him! And I'm not ungrateful, I don't like my engagement ring because it is the same as his ex's ring!!! Am I overreacting? Sometimes I feel like he is trying to replace her with me. We've been together for 2 years they were together for 7 years and she cheated on him more then 5 times... He always talks about things they used to do together! What should I do!!!