I haven't told the father.plz help.

I'm about 16 weeks pregnant from my ex. We broke up someone in April but we kept seeing each other till about August because we broke up every time we did see each other it was fighting and more fighting so we completely stopped, but I had a laps of judgement and slept with him again in October when I got pregnant. I didn't take a test till about December by then we aren't talking at all. I know I should tell him I just have no idea how to.