What should i do about this man i have fallen in love with but he already has a girlfriend?

We met unexpectedly by mishap. The day i met him i was looking for my son because that was the last place i dropped him off for school our sons were friends. How we meet was i had gotten a call from the school stating that my son was not there so i went to the place where i had dropped him off to catch the bus. This guy answered the door after me knocking for a while. I was so upset i didn't notice him at all. I called the school back and they checked his classes and a few minutes after i had left this guy house they said he was in class they had made a mistake. So i went back to work later that afternoon i got a call from this guy i had meet earlier stating that my son was at his house do i need to talk him and i told him about the school making a mistake and i was sorry for banging on his doors so hard. When i got there to pick my son up he was the one came out of the house to ask me was it all right for my son to go out to eat with him and his son if it was okay with my other half i told him there was no other half just me he even offered to bring him home. The next day i called him to thank him for bringing him home he told me i was welcome and i could call him any time. The next day i called him but he wasn't home but later that night he called me and we talked for about a hour on the phone. We started talking on a regular bases he then gave me his cell phone number. He then wanted hugs from me which he would drive all the way to my house and get then it lead to kissing and we really like one another but really wanted to keep it at a friendship level because he did mention he had a friend but nothing was serious between them. It really didn't matter to me because i wasn't looking for a boyfriend just someone to talk to.But we grew to love one another. Right now he considers me as his woman even though he says he loves his girlfriend and tell me he loves me too and he don't want to let me go he wants to keep both of us. But after months of feeling hurt because he is with her and then he spends time with me but not as much as i would like. But i have gotten to the point i can no longer deal with it and i broke off the relationship but i love him and my heart is broken i want to make sure i did the right thing even though i hate to see him hurting but i can no longer deal with it because i want my own man i can love and be with and not have to share. I really love him but i cant have him he always says the only difference between me and his girlfriend is he meet her first and that we are both wonderful women. Please give me the best advice you possibly can i hope i explained it clearly there is so much that i can tell u but i tried to narrow it down as much as i could. Please give me your best advice.What should i do about this man i have fallen in love with but he already has a girlfriend?
if he's going to cheat on her, he'll just cheat on you. get over it and move on.