If your boyfriend liked your best friend before you?

So. My boyfriend that I love, really liked my bff before me. Its hard cause they are close so I feel like he will develop feelings for her again. He used to walk her home, she would be all over him too, but claim she never liked him, even though a lot of people think she did. She has a bf, and did before but still tickled him and hugged him and was like clingy about him. I feel slightly insecure about it and am worried that he will like her again? Help??? I know it's the past, but i am worried.