She left me for someone else?

ok where do i start we had been togetheir nearly 10 years and have a 6 year old son and was very happy untill one night i went out and was with the boys from a footie team and got chatting to a group of girls i have never cheated and never will but unfortunutly there was a 18 year girl who would not leave me alone i told her i was 30 and find someone else plenty of guys in here i have a goergous women who i am happy with, i went home that night and thought nothing more of it then a few days later she messeged me on facebook and i never had anything to hide so my partner was always on there but the girl messeged as if something happened now i live in a small town so she got my name from her freinds obviously my partner thought i had done something i pleaded my innocence but knew it looked bad 2 weeks later she went out met someone cheated on me and finished our relationship and was smitten by this new bloke.it turns out he was cheating on her so not with her now so how do i get her back