College Student wondering: Should I be wary of my boyfriend's 8th grade crush?

My boyfriend of 5 years still keeps in touch with a girl he "dated" in 8th grade for a week while he was 13. We are now 20 and he calls her just a friend (which I have still never met). She has called him to talk on the phone and hang out just as friends occasionally over the past 7 years. I never really took notice of their relationship until recently when he deceived me about seeing her. His "ex"/friend called him one night around 9:30 while we were together and he cut the conversation with her short after seeing my unhappy facial expression. Turns out after I left, he called her back arranging a hang out with 2 of his other male friends. He failed to mention her involvement in his hang out plans that day and I didn't find out she was even there until I saw it on one of his text messages. He claims they are just friends, that she has a boyfriend and that she knows that he is dating me. I just get paranoid thinking he might have "first-love" feelings towards her (since she broke off their week long relationship) or that they might still have a flirting attraction to each other. Either way, whatever the truth is, it makes me uncomfortable knowing she calls him, or vice versa, still wanting to hang out or catch up.I mean it was a middle school crush, how are they still good friends? What is the relationship really? Should I be concerned?