When u love someone u let them go if they come back then it was meant to be- but what happens ur both married and have total different lives now

I have a big problem! It all starts when I was young I met a boy and we dated off and on for six years but we were always moving so it made it difficult for us to date. Then he decided to join the army so he left for bootcamp. I was devistated and I wrote to him but never recieved nothing back. A year went by and I was still not over him but sum ppl thought it was best for me to move on with my life so I did. I met a guy and we got married and had four kids. This old boyfriend never left my heart cuz he was my first love and I thought bout him all the time. Just a few months ago he appeared in my life again but only online. I t turns out he never got my letters and hes been looking for me ever since. Although he is now married and has two kids. He wants to meet with me and he says he still madly in love with me. I dont know what to do cuz ive been talking to him and I think im in love all over again with this man. I have a wonderful husband but im kinda in a difficult situation. H e says he isnt happy with his wife becuz he belives he belongs with me but its so hard to figure out what will we do about our families. im confused and idk what to do I let him go cuz I loved him but now that hes back its hard to be together again.