How do you tell your boyfriend you're pregnant with another guy's baby?
It's a little late isn't it! You know better and you're basically immature and if you had lost feelings for your boyfriend then you should have broken up with him before seeing another guy. Face the music and be responsible for your own actions!
No matter how you tell him it's going hurt. Some guys (depending if it's the first time their girlfriend/wife had an affair) are willing to forgive and forget and help raise the child (they are few and far between though) and if he is one of these guys consider yourself lucky. However, it's only right you tell the baby's father it's his child (if you know for sure.)
Face the music!
theres no easy way to tell him this happen to me she told me she the baby was mine we got married. and 6 months in she told the cops i hit her. and they belived her cuz of my anger mangment class a use to take. i go to jail amd she gets her green card then i found out its not mine.