How to accept the fact that my boyfriend had a relationship before me?

He told me that they had kind of a toxic relationship, it lasted just few months, she told him that she didn't love him anymore and left, yet it bothers me so much because I'm not his first everything and I want to prove to myself and to him that I'm so much better than she is even tho I'm comparing myself to the woman I've never met. He also keeps mentioning her now and then, what she did that I don't do, he wants me to visit the city where she lives but I refused etc and those things just make me even angrier.
How to accept the fact that my boyfriend had a relationship before me?
How to accept the fact that my boyfriend had a relationship before me?
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