Tell him you have something very important to talk to him about in private, just you and him. Be prepared for some men say it's not his and so on. If you decide to keep the child get a D.N.A. TEST when the child gets older the baby may look like him too. Some men will step up to the plate and help you look after the baby some turn and RUN and call you names. But you know who's baby it is and the child will always love you for you are the baby's mother. My child's father hasn't been in his life for 34 years my son loves me and I will love my son til the day I die I would never give him up he's my son, yes he ask about his father and I tell him the truth I don't lie to him. If he ever wishes to meet him he can I told my son everything about his father and I when we were dating. It's better to tell the truth then lie I find. My son spoke to his father ones on the phone and his father to this day says he's NOT my son's dad. To bad it's his loss for he has a wonderful son he'll never know and he's not in his life and sees his grandchild who is how three.
In my opinion there are various methods you can use to inform your ex boyfriend you are pregnant. You can call him and tell him you need to have an urgent conversation, you can tell one of his reliable sources to organize am meet or even call and break the news.
There is not going to be an easy way to tell him, even if he was not your ex. Just call, ask to meet him and get it over with. I would not expect jumping for joy. Hope for support, but be prepared for shock, denial, anger, and accusations.
What I did was went to his house and told him to his face, we sat in his room and I just started crying and told him. (we never dates again, which was fine with me and he's never been in my son life who is now 15) so don't expect too much. Also go over there with some type of proof so he doesn't call you a liar.
Decide first what you want from him. Do you need money to help raise his child? Do you want him to be part of the child's life? Are you hoping he will want you back? The law is available if you need it to extract the money your child needs.