My bikini top fell off at the beach? Please help me?

My boyfriend, his friends, and I went to the beach today. The knot behind my neck fell undone when I was in a sand fight with one of his friends and my boyfriend. His friend tackled me and it untied (it was already loose from tackling my boyfriend so it was a complete accident) I covered myself up immediately once I noticed and got super embarrassed. My boyfriend on the other hand got pissed off. He shoved his friend off of me and started yelling at him. I got him to calm down but he is still mad at his friend because he saw me and didn't advert his eyes before I was able to cover up. How can I get him to forgive his friend and get over all of this?
My bikini top fell off at the beach? Please help me?
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