What do I do I had sex with someones boyfriend?

dont go their , unless your a spiteful back stabbing tart, whether you lie his girlfriend ro not some one willg et hurt and its most likely you as this lad is using you both, open your eyes hun and see he doesnt care about your feeligns or the other girls just his self. Give him a choice fi eh really likes you and wants you not this otehr gril then he will finish with her before , don’t rush into this though and keep your legs crossed he he make him wait till he realises what eh wants and that your not soem oen who will come runnign when he clicks his fingers its not all about his needs is it, if you lvoe him you will give him the chance to walk away from you lets be honest if eh lvoed the other girl he wouldnt be cheating on erh and if he lvoed you he wouldnt have this otehr girl on the go so all I can say is giv it time you will meet some worth lovign and he well he will still be messign girls around till he gets found out and no oen will trust him but once a cheat always a cheat whether its you his cheating on or someone else he wont change he sounds to selfish to change or to care about anyone else ! good luck with it all x