What do you do when youre still in love with the boy who broke your heart?

Okay, this is kind of complicated. I am married and love my husband with all my heart. I couldnt ask for anyone more loving and kind. But, Im afraid I still have strong feelings for a boy who broke my heart over 5 years ago. You see, he is my husbands best friend. I met them both at the same time, and at that time my now husband was dating someone else and the other boy was single and so was I. From the moment I first saw him I felt something spark inside me. It was like love at first sight. The first time we kissed was amazing, I mean after we pulled away from the kiss he says to me “wow did you feel that?”.. we just had such a strong, intense connection from the begining. But the timing wasnt right and we decided to end things. We didnt date very long, but the feelings were all there. It was so intense. Then three months after that, I began dating my now husband and as you see, we’re married. But this boy is my husbands best friend. He is always around. I never fully got over him. He still flirts with me, tells me he thinks Im beautiful, tells me about the first time he saw me walking up to him and how he thought I was the most beautiful thing he ever saw. There is still a connection there but Im married now and I keep telling myself to let it go but I cant.. can anyone give me some advice on what to do to let this go fully. I know I shouldnt have these feelings for someone else, but no matter what I do I still think about him..